Hello!
This patchset is an update of that posted by Dipankar last January
(http://lkml.org/lkml/2007/1/15/133). This is work in progress, not yet
ready for inclusion. It passes rcutorture on i386, x86_64, and ppc64
boxes as well as kernbench, so should be safe for experimentation. As
with Dipankar's previous post, this variant of preemptible rcu_read_lock()
and rcu_read_unlock may be invoked from NMI/SMI handlers, and do not
contain any heavyweight atomic operations or memory barriers (although
they do still momentarily disable IRQs). This patchset features
a fully parallel grace-period computation, which will become increasingly
important with upcoming multicore/multi-threaded CPUs. In addition,
this patchset provides a preemptible-RCU variant of synchronize_sched()
that avoids the previous deadlock with CPU hotplug -- this variant may
eventually prove unnecessary, but is offered in the spirit of separating
concerns.
Next steps: (1) Integrate with CPU hotplug. (2) Re-merge RCU priority
boosting. (3) Fix some naming issues. Longer term work includes
optimized dyntick operation and eliminating the interrupt disabling
in rcu_read_lock() and rcu_read_unlock().
Thanx, Paul
This patch re-organizes the RCU code to enable multiple implementations
of RCU. Users of RCU continues to include rcupdate.h and the
RCU interfaces remain the same. This is in preparation for
subsequently merging the preepmtpible RCU implementation.
Signed-off-by: Dipankar Sarma <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
---
include/linux/rcuclassic.h | 149 ++++++++++++
include/linux/rcupdate.h | 151 +++---------
kernel/Makefile | 2
kernel/rcuclassic.c | 558 +++++++++++++++++++++++++++++++++++++++++++++
kernel/rcupdate.c | 558 ++-------------------------------------------
5 files changed, 778 insertions(+), 640 deletions(-)
diff -urpNa -X dontdiff linux-2.6.22/include/linux/rcuclassic.h linux-2.6.22-a-splitclassic/include/linux/rcuclassic.h
--- linux-2.6.22/include/linux/rcuclassic.h 1969-12-31 16:00:00.000000000 -0800
+++ linux-2.6.22-a-splitclassic/include/linux/rcuclassic.h 2007-07-19 14:19:00.000000000 -0700
@@ -0,0 +1,149 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion (classic version)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2001
+ *
+ * Author: Dipankar Sarma <[email protected]>
+ *
+ * Based on the original work by Paul McKenney <[email protected]>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU
+ *
+ */
+
+#ifndef __LINUX_RCUCLASSIC_H
+#define __LINUX_RCUCLASSIC_H
+
+#ifdef __KERNEL__
+
+#include <linux/cache.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+#include <linux/percpu.h>
+#include <linux/cpumask.h>
+#include <linux/seqlock.h>
+
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+ long cur; /* Current batch number. */
+ long completed; /* Number of the last completed batch */
+ int next_pending; /* Is the next batch already waiting? */
+
+ int signaled;
+
+ spinlock_t lock ____cacheline_internodealigned_in_smp;
+ cpumask_t cpumask; /* CPUs that need to switch in order */
+ /* for current batch to proceed. */
+} ____cacheline_internodealigned_in_smp;
+
+/* Is batch a before batch b ? */
+static inline int rcu_batch_before(long a, long b)
+{
+ return (a - b) < 0;
+}
+
+/* Is batch a after batch b ? */
+static inline int rcu_batch_after(long a, long b)
+{
+ return (a - b) > 0;
+}
+
+/*
+ * Per-CPU data for Read-Copy UPdate.
+ * nxtlist - new callbacks are added here
+ * curlist - current batch for which quiescent cycle started if any
+ */
+struct rcu_data {
+ /* 1) quiescent state handling : */
+ long quiescbatch; /* Batch # for grace period */
+ int passed_quiesc; /* User-mode/idle loop etc. */
+ int qs_pending; /* core waits for quiesc state */
+
+ /* 2) batch handling */
+ long batch; /* Batch # for current RCU batch */
+ struct rcu_head *nxtlist;
+ struct rcu_head **nxttail;
+ long qlen; /* # of queued callbacks */
+ struct rcu_head *curlist;
+ struct rcu_head **curtail;
+ struct rcu_head *donelist;
+ struct rcu_head **donetail;
+ long blimit; /* Upper limit on a processed batch */
+ int cpu;
+ struct rcu_head barrier;
+};
+
+DECLARE_PER_CPU(struct rcu_data, rcu_data);
+DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
+
+/*
+ * Increment the quiescent state counter.
+ * The counter is a bit degenerated: We do not need to know
+ * how many quiescent states passed, just if there was at least
+ * one since the start of the grace period. Thus just a flag.
+ */
+static inline void rcu_qsctr_inc(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ rdp->passed_quiesc = 1;
+}
+static inline void rcu_bh_qsctr_inc(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
+ rdp->passed_quiesc = 1;
+}
+
+extern int rcu_pending(int cpu);
+extern int rcu_needs_cpu(int cpu);
+
+#define __rcu_read_lock() \
+ do { \
+ preempt_disable(); \
+ __acquire(RCU); \
+ } while(0)
+#define __rcu_read_unlock() \
+ do { \
+ __release(RCU); \
+ preempt_enable(); \
+ } while(0)
+#define __rcu_read_lock_bh() \
+ do { \
+ local_bh_disable(); \
+ __acquire(RCU_BH); \
+ } while(0)
+#define __rcu_read_unlock_bh() \
+ do { \
+ __release(RCU_BH); \
+ local_bh_enable(); \
+ } while(0)
+
+#define __synchronize_sched() synchronize_rcu()
+
+extern void __rcu_init(void);
+extern void rcu_check_callbacks(int cpu, int user);
+extern void rcu_restart_cpu(int cpu);
+extern long rcu_batches_completed(void);
+extern long rcu_batches_completed_bh(void);
+
+#endif /* __KERNEL__ */
+#endif /* __LINUX_RCUCLASSIC_H */
diff -urpNa -X dontdiff linux-2.6.22/include/linux/rcupdate.h linux-2.6.22-a-splitclassic/include/linux/rcupdate.h
--- linux-2.6.22/include/linux/rcupdate.h 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-a-splitclassic/include/linux/rcupdate.h 2007-07-19 14:02:36.000000000 -0700
@@ -15,7 +15,7 @@
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
- * Copyright (C) IBM Corporation, 2001
+ * Copyright IBM Corporation, 2001
*
* Author: Dipankar Sarma <[email protected]>
*
@@ -52,6 +52,8 @@ struct rcu_head {
void (*func)(struct rcu_head *head);
};
+#include <linux/rcuclassic.h>
+
#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
#define INIT_RCU_HEAD(ptr) do { \
@@ -59,80 +61,6 @@ struct rcu_head {
} while (0)
-
-/* Global control variables for rcupdate callback mechanism. */
-struct rcu_ctrlblk {
- long cur; /* Current batch number. */
- long completed; /* Number of the last completed batch */
- int next_pending; /* Is the next batch already waiting? */
-
- int signaled;
-
- spinlock_t lock ____cacheline_internodealigned_in_smp;
- cpumask_t cpumask; /* CPUs that need to switch in order */
- /* for current batch to proceed. */
-} ____cacheline_internodealigned_in_smp;
-
-/* Is batch a before batch b ? */
-static inline int rcu_batch_before(long a, long b)
-{
- return (a - b) < 0;
-}
-
-/* Is batch a after batch b ? */
-static inline int rcu_batch_after(long a, long b)
-{
- return (a - b) > 0;
-}
-
-/*
- * Per-CPU data for Read-Copy UPdate.
- * nxtlist - new callbacks are added here
- * curlist - current batch for which quiescent cycle started if any
- */
-struct rcu_data {
- /* 1) quiescent state handling : */
- long quiescbatch; /* Batch # for grace period */
- int passed_quiesc; /* User-mode/idle loop etc. */
- int qs_pending; /* core waits for quiesc state */
-
- /* 2) batch handling */
- long batch; /* Batch # for current RCU batch */
- struct rcu_head *nxtlist;
- struct rcu_head **nxttail;
- long qlen; /* # of queued callbacks */
- struct rcu_head *curlist;
- struct rcu_head **curtail;
- struct rcu_head *donelist;
- struct rcu_head **donetail;
- long blimit; /* Upper limit on a processed batch */
- int cpu;
- struct rcu_head barrier;
-};
-
-DECLARE_PER_CPU(struct rcu_data, rcu_data);
-DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
-
-/*
- * Increment the quiescent state counter.
- * The counter is a bit degenerated: We do not need to know
- * how many quiescent states passed, just if there was at least
- * one since the start of the grace period. Thus just a flag.
- */
-static inline void rcu_qsctr_inc(int cpu)
-{
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- rdp->passed_quiesc = 1;
-}
-static inline void rcu_bh_qsctr_inc(int cpu)
-{
- struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
- rdp->passed_quiesc = 1;
-}
-
-extern int rcu_pending(int cpu);
-extern int rcu_needs_cpu(int cpu);
-
/**
* rcu_read_lock - mark the beginning of an RCU read-side critical section.
*
@@ -162,22 +90,14 @@ extern int rcu_needs_cpu(int cpu);
*
* It is illegal to block while in an RCU read-side critical section.
*/
-#define rcu_read_lock() \
- do { \
- preempt_disable(); \
- __acquire(RCU); \
- } while(0)
+#define rcu_read_lock() __rcu_read_lock()
/**
* rcu_read_unlock - marks the end of an RCU read-side critical section.
*
* See rcu_read_lock() for more information.
*/
-#define rcu_read_unlock() \
- do { \
- __release(RCU); \
- preempt_enable(); \
- } while(0)
+#define rcu_read_unlock() __rcu_read_unlock()
/*
* So where is rcu_write_lock()? It does not exist, as there is no
@@ -200,22 +120,14 @@ extern int rcu_needs_cpu(int cpu);
* can use just rcu_read_lock().
*
*/
-#define rcu_read_lock_bh() \
- do { \
- local_bh_disable(); \
- __acquire(RCU_BH); \
- } while(0)
+#define rcu_read_lock_bh() __rcu_read_lock_bh()
/*
* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
*
* See rcu_read_lock_bh() for more information.
*/
-#define rcu_read_unlock_bh() \
- do { \
- __release(RCU_BH); \
- local_bh_enable(); \
- } while(0)
+#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
/**
* rcu_dereference - fetch an RCU-protected pointer in an
@@ -267,22 +179,49 @@ extern int rcu_needs_cpu(int cpu);
* In "classic RCU", these two guarantees happen to be one and
* the same, but can differ in realtime RCU implementations.
*/
-#define synchronize_sched() synchronize_rcu()
+#define synchronize_sched() __synchronize_sched()
-extern void rcu_init(void);
-extern void rcu_check_callbacks(int cpu, int user);
-extern void rcu_restart_cpu(int cpu);
-extern long rcu_batches_completed(void);
-extern long rcu_batches_completed_bh(void);
-
-/* Exported interfaces */
-extern void FASTCALL(call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *head)));
+/**
+ * call_rcu - Queue an RCU callback for invocation after a grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual update function to be invoked after the grace period
+ *
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ */
+extern void FASTCALL(call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *head)));
+
+/**
+ * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual update function to be invoked after the grace period
+ *
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_bh() assumes
+ * that the read-side critical sections end on completion of a softirq
+ * handler. This means that read-side critical sections in process
+ * context must not be interrupted by softirqs. This interface is to be
+ * used when most of the read-side critical sections are in softirq context.
+ * RCU read-side critical sections are delimited by rcu_read_lock() and
+ * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
+ * and rcu_read_unlock_bh(), if in process context. These may be nested.
+ */
extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
void (*func)(struct rcu_head *head)));
+
+/* Exported common interfaces */
extern void synchronize_rcu(void);
-void synchronize_idle(void);
extern void rcu_barrier(void);
+/* Internal to kernel */
+extern void rcu_init(void);
+extern void rcu_check_callbacks(int cpu, int user);
+
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPDATE_H */
diff -urpNa -X dontdiff linux-2.6.22/kernel/Makefile linux-2.6.22-a-splitclassic/kernel/Makefile
--- linux-2.6.22/kernel/Makefile 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-a-splitclassic/kernel/Makefile 2007-07-19 12:16:03.000000000 -0700
@@ -6,7 +6,7 @@ obj-y = sched.o fork.o exec_domain.o
exit.o itimer.o time.o softirq.o resource.o \
sysctl.o capability.o ptrace.o timer.o user.o \
signal.o sys.o kmod.o workqueue.o pid.o \
- rcupdate.o extable.o params.o posix-timers.o \
+ rcupdate.o rcuclassic.o extable.o params.o posix-timers.o \
kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
hrtimer.o rwsem.o latency.o nsproxy.o srcu.o die_notifier.o
diff -urpNa -X dontdiff linux-2.6.22/kernel/rcuclassic.c linux-2.6.22-a-splitclassic/kernel/rcuclassic.c
--- linux-2.6.22/kernel/rcuclassic.c 1969-12-31 16:00:00.000000000 -0800
+++ linux-2.6.22-a-splitclassic/kernel/rcuclassic.c 2007-07-19 15:03:51.000000000 -0700
@@ -0,0 +1,558 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2001
+ *
+ * Authors: Dipankar Sarma <[email protected]>
+ * Manfred Spraul <[email protected]>
+ *
+ * Based on the original work by Paul McKenney <[email protected]>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU
+ *
+ */
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <asm/atomic.h>
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <linux/completion.h>
+#include <linux/moduleparam.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+/* #include <linux/rcupdate.h> @@@ */
+#include <linux/cpu.h>
+#include <linux/mutex.h>
+
+/* Definition for rcupdate control block. */
+static struct rcu_ctrlblk rcu_ctrlblk = {
+ .cur = -300,
+ .completed = -300,
+ .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
+ .cpumask = CPU_MASK_NONE,
+};
+static struct rcu_ctrlblk rcu_bh_ctrlblk = {
+ .cur = -300,
+ .completed = -300,
+ .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
+ .cpumask = CPU_MASK_NONE,
+};
+
+DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
+DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
+
+/* Fake initialization required by compiler */
+static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
+static int blimit = 10;
+static int qhimark = 10000;
+static int qlowmark = 100;
+
+#ifdef CONFIG_SMP
+static void force_quiescent_state(struct rcu_data *rdp,
+ struct rcu_ctrlblk *rcp)
+{
+ int cpu;
+ cpumask_t cpumask;
+ set_need_resched();
+ if (unlikely(!rcp->signaled)) {
+ rcp->signaled = 1;
+ /*
+ * Don't send IPI to itself. With irqs disabled,
+ * rdp->cpu is the current cpu.
+ */
+ cpumask = rcp->cpumask;
+ cpu_clear(rdp->cpu, cpumask);
+ for_each_cpu_mask(cpu, cpumask)
+ smp_send_reschedule(cpu);
+ }
+}
+#else
+static inline void force_quiescent_state(struct rcu_data *rdp,
+ struct rcu_ctrlblk *rcp)
+{
+ set_need_resched();
+}
+#endif
+
+/**
+ * call_rcu - Queue an RCU callback for invocation after a grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual update function to be invoked after the grace period
+ *
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ */
+void fastcall call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+
+ head->func = func;
+ head->next = NULL;
+ local_irq_save(flags);
+ rdp = &__get_cpu_var(rcu_data);
+ *rdp->nxttail = head;
+ rdp->nxttail = &head->next;
+ if (unlikely(++rdp->qlen > qhimark)) {
+ rdp->blimit = INT_MAX;
+ force_quiescent_state(rdp, &rcu_ctrlblk);
+ }
+ local_irq_restore(flags);
+}
+
+/**
+ * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual update function to be invoked after the grace period
+ *
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_bh() assumes
+ * that the read-side critical sections end on completion of a softirq
+ * handler. This means that read-side critical sections in process
+ * context must not be interrupted by softirqs. This interface is to be
+ * used when most of the read-side critical sections are in softirq context.
+ * RCU read-side critical sections are delimited by rcu_read_lock() and
+ * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
+ * and rcu_read_unlock_bh(), if in process context. These may be nested.
+ */
+void fastcall call_rcu_bh(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+
+ head->func = func;
+ head->next = NULL;
+ local_irq_save(flags);
+ rdp = &__get_cpu_var(rcu_bh_data);
+ *rdp->nxttail = head;
+ rdp->nxttail = &head->next;
+
+ if (unlikely(++rdp->qlen > qhimark)) {
+ rdp->blimit = INT_MAX;
+ force_quiescent_state(rdp, &rcu_bh_ctrlblk);
+ }
+
+ local_irq_restore(flags);
+}
+
+/*
+ * Return the number of RCU batches processed thus far. Useful
+ * for debug and statistics.
+ */
+long rcu_batches_completed(void)
+{
+ return rcu_ctrlblk.completed;
+}
+
+/*
+ * Return the number of RCU batches processed thus far. Useful
+ * for debug and statistics.
+ */
+long rcu_batches_completed_bh(void)
+{
+ return rcu_bh_ctrlblk.completed;
+}
+
+/*
+ * Invoke the completed RCU callbacks. They are expected to be in
+ * a per-cpu list.
+ */
+static void rcu_do_batch(struct rcu_data *rdp)
+{
+ struct rcu_head *next, *list;
+ int count = 0;
+
+ list = rdp->donelist;
+ while (list) {
+ next = list->next;
+ prefetch(next);
+ list->func(list);
+ list = next;
+ if (++count >= rdp->blimit)
+ break;
+ }
+ rdp->donelist = list;
+
+ local_irq_disable();
+ rdp->qlen -= count;
+ local_irq_enable();
+ if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
+ rdp->blimit = blimit;
+
+ if (!rdp->donelist)
+ rdp->donetail = &rdp->donelist;
+ else
+ tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
+}
+
+/*
+ * Grace period handling:
+ * The grace period handling consists out of two steps:
+ * - A new grace period is started.
+ * This is done by rcu_start_batch. The start is not broadcasted to
+ * all cpus, they must pick this up by comparing rcp->cur with
+ * rdp->quiescbatch. All cpus are recorded in the
+ * rcu_ctrlblk.cpumask bitmap.
+ * - All cpus must go through a quiescent state.
+ * Since the start of the grace period is not broadcasted, at least two
+ * calls to rcu_check_quiescent_state are required:
+ * The first call just notices that a new grace period is running. The
+ * following calls check if there was a quiescent state since the beginning
+ * of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
+ * the bitmap is empty, then the grace period is completed.
+ * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
+ * period (if necessary).
+ */
+/*
+ * Register a new batch of callbacks, and start it up if there is currently no
+ * active batch and the batch to be registered has not already occurred.
+ * Caller must hold rcu_ctrlblk.lock.
+ */
+static void rcu_start_batch(struct rcu_ctrlblk *rcp)
+{
+ if (rcp->next_pending &&
+ rcp->completed == rcp->cur) {
+ rcp->next_pending = 0;
+ /*
+ * next_pending == 0 must be visible in
+ * __rcu_process_callbacks() before it can see new value of cur.
+ */
+ smp_wmb();
+ rcp->cur++;
+
+ /*
+ * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
+ * Barrier Otherwise it can cause tickless idle CPUs to be
+ * included in rcp->cpumask, which will extend graceperiods
+ * unnecessarily.
+ */
+ smp_mb();
+ cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
+
+ rcp->signaled = 0;
+ }
+}
+
+/*
+ * cpu went through a quiescent state since the beginning of the grace period.
+ * Clear it from the cpu mask and complete the grace period if it was the last
+ * cpu. Start another grace period if someone has further entries pending
+ */
+static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
+{
+ cpu_clear(cpu, rcp->cpumask);
+ if (cpus_empty(rcp->cpumask)) {
+ /* batch completed ! */
+ rcp->completed = rcp->cur;
+ rcu_start_batch(rcp);
+ }
+}
+
+/*
+ * Check if the cpu has gone through a quiescent state (say context
+ * switch). If so and if it already hasn't done so in this RCU
+ * quiescent cycle, then indicate that it has done so.
+ */
+static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ if (rdp->quiescbatch != rcp->cur) {
+ /* start new grace period: */
+ rdp->qs_pending = 1;
+ rdp->passed_quiesc = 0;
+ rdp->quiescbatch = rcp->cur;
+ return;
+ }
+
+ /* Grace period already completed for this cpu?
+ * qs_pending is checked instead of the actual bitmap to avoid
+ * cacheline trashing.
+ */
+ if (!rdp->qs_pending)
+ return;
+
+ /*
+ * Was there a quiescent state since the beginning of the grace
+ * period? If no, then exit and wait for the next call.
+ */
+ if (!rdp->passed_quiesc)
+ return;
+ rdp->qs_pending = 0;
+
+ spin_lock(&rcp->lock);
+ /*
+ * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
+ * during cpu startup. Ignore the quiescent state.
+ */
+ if (likely(rdp->quiescbatch == rcp->cur))
+ cpu_quiet(rdp->cpu, rcp);
+
+ spin_unlock(&rcp->lock);
+}
+
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+/* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
+ * locking requirements, the list it's pulling from has to belong to a cpu
+ * which is dead and hence not processing interrupts.
+ */
+static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
+ struct rcu_head **tail)
+{
+ local_irq_disable();
+ *this_rdp->nxttail = list;
+ if (list)
+ this_rdp->nxttail = tail;
+ local_irq_enable();
+}
+
+static void __rcu_offline_cpu(struct rcu_data *this_rdp,
+ struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
+{
+ /* if the cpu going offline owns the grace period
+ * we can block indefinitely waiting for it, so flush
+ * it here
+ */
+ spin_lock_bh(&rcp->lock);
+ if (rcp->cur != rcp->completed)
+ cpu_quiet(rdp->cpu, rcp);
+ spin_unlock_bh(&rcp->lock);
+ rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
+ rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
+ rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
+}
+
+static void rcu_offline_cpu(int cpu)
+{
+ struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
+ struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
+
+ __rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
+ &per_cpu(rcu_data, cpu));
+ __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
+ &per_cpu(rcu_bh_data, cpu));
+ put_cpu_var(rcu_data);
+ put_cpu_var(rcu_bh_data);
+ tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
+}
+
+#else
+
+static void rcu_offline_cpu(int cpu)
+{
+}
+
+#endif
+
+/*
+ * This does the RCU processing work from tasklet context.
+ */
+static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
+ *rdp->donetail = rdp->curlist;
+ rdp->donetail = rdp->curtail;
+ rdp->curlist = NULL;
+ rdp->curtail = &rdp->curlist;
+ }
+
+ if (rdp->nxtlist && !rdp->curlist) {
+ local_irq_disable();
+ rdp->curlist = rdp->nxtlist;
+ rdp->curtail = rdp->nxttail;
+ rdp->nxtlist = NULL;
+ rdp->nxttail = &rdp->nxtlist;
+ local_irq_enable();
+
+ /*
+ * start the next batch of callbacks
+ */
+
+ /* determine batch number */
+ rdp->batch = rcp->cur + 1;
+ /* see the comment and corresponding wmb() in
+ * the rcu_start_batch()
+ */
+ smp_rmb();
+
+ if (!rcp->next_pending) {
+ /* and start it/schedule start if it's a new batch */
+ spin_lock(&rcp->lock);
+ rcp->next_pending = 1;
+ rcu_start_batch(rcp);
+ spin_unlock(&rcp->lock);
+ }
+ }
+
+ rcu_check_quiescent_state(rcp, rdp);
+ if (rdp->donelist)
+ rcu_do_batch(rdp);
+}
+
+static void rcu_process_callbacks(unsigned long unused)
+{
+ __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
+ __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
+}
+
+static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
+{
+ /* This cpu has pending rcu entries and the grace period
+ * for them has completed.
+ */
+ if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
+ return 1;
+
+ /* This cpu has no pending entries, but there are new entries */
+ if (!rdp->curlist && rdp->nxtlist)
+ return 1;
+
+ /* This cpu has finished callbacks to invoke */
+ if (rdp->donelist)
+ return 1;
+
+ /* The rcu core waits for a quiescent state from the cpu */
+ if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
+ return 1;
+
+ /* nothing to do */
+ return 0;
+}
+
+/*
+ * Check to see if there is any immediate RCU-related work to be done
+ * by the current CPU, returning 1 if so. This function is part of the
+ * RCU implementation; it is -not- an exported member of the RCU API.
+ */
+int rcu_pending(int cpu)
+{
+ return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
+ __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
+}
+
+/*
+ * Check to see if any future RCU-related work will need to be done
+ * by the current CPU, even if none need be done immediately, returning
+ * 1 if so. This function is part of the RCU implementation; it is -not-
+ * an exported member of the RCU API.
+ */
+int rcu_needs_cpu(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
+
+ return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
+}
+
+void rcu_check_callbacks(int cpu, int user)
+{
+ if (user ||
+ (idle_cpu(cpu) && !in_softirq() &&
+ hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
+ rcu_qsctr_inc(cpu);
+ rcu_bh_qsctr_inc(cpu);
+ } else if (!in_softirq())
+ rcu_bh_qsctr_inc(cpu);
+ tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
+}
+
+static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ memset(rdp, 0, sizeof(*rdp));
+ rdp->curtail = &rdp->curlist;
+ rdp->nxttail = &rdp->nxtlist;
+ rdp->donetail = &rdp->donelist;
+ rdp->quiescbatch = rcp->completed;
+ rdp->qs_pending = 0;
+ rdp->cpu = cpu;
+ rdp->blimit = blimit;
+}
+
+static void __devinit rcu_online_cpu(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
+
+ rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
+ rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
+ tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
+}
+
+static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ long cpu = (long)hcpu;
+ switch (action) {
+ case CPU_UP_PREPARE:
+ case CPU_UP_PREPARE_FROZEN:
+ rcu_online_cpu(cpu);
+ break;
+ case CPU_DEAD:
+ case CPU_DEAD_FROZEN:
+ rcu_offline_cpu(cpu);
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata rcu_nb = {
+ .notifier_call = rcu_cpu_notify,
+};
+
+/*
+ * Initializes rcu mechanism. Assumed to be called early.
+ * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
+ * Note that rcu_qsctr and friends are implicitly
+ * initialized due to the choice of ``0'' for RCU_CTR_INVALID.
+ */
+void __init __rcu_init(void)
+{
+ rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
+ (void *)(long)smp_processor_id());
+ /* Register notifier for non-boot CPUs */
+ register_cpu_notifier(&rcu_nb);
+}
+
+module_param(blimit, int, 0);
+module_param(qhimark, int, 0);
+module_param(qlowmark, int, 0);
+EXPORT_SYMBOL_GPL(rcu_batches_completed);
+EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
+EXPORT_SYMBOL_GPL(call_rcu);
+EXPORT_SYMBOL_GPL(call_rcu_bh);
diff -urpNa -X dontdiff linux-2.6.22/kernel/rcupdate.c linux-2.6.22-a-splitclassic/kernel/rcupdate.c
--- linux-2.6.22/kernel/rcupdate.c 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-a-splitclassic/kernel/rcupdate.c 2007-07-19 14:19:03.000000000 -0700
@@ -15,7 +15,7 @@
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
- * Copyright (C) IBM Corporation, 2001
+ * Copyright IBM Corporation, 2001
*
* Authors: Dipankar Sarma <[email protected]>
* Manfred Spraul <[email protected]>
@@ -35,157 +35,56 @@
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
-#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <asm/atomic.h>
#include <linux/bitops.h>
-#include <linux/module.h>
#include <linux/completion.h>
-#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
+#include <linux/module.h>
-/* Definition for rcupdate control block. */
-static struct rcu_ctrlblk rcu_ctrlblk = {
- .cur = -300,
- .completed = -300,
- .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
- .cpumask = CPU_MASK_NONE,
-};
-static struct rcu_ctrlblk rcu_bh_ctrlblk = {
- .cur = -300,
- .completed = -300,
- .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
- .cpumask = CPU_MASK_NONE,
+struct rcu_synchronize {
+ struct rcu_head head;
+ struct completion completion;
};
-DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
-DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
-
-/* Fake initialization required by compiler */
-static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
-static int blimit = 10;
-static int qhimark = 10000;
-static int qlowmark = 100;
-
+static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
static atomic_t rcu_barrier_cpu_count;
static DEFINE_MUTEX(rcu_barrier_mutex);
static struct completion rcu_barrier_completion;
-#ifdef CONFIG_SMP
-static void force_quiescent_state(struct rcu_data *rdp,
- struct rcu_ctrlblk *rcp)
-{
- int cpu;
- cpumask_t cpumask;
- set_need_resched();
- if (unlikely(!rcp->signaled)) {
- rcp->signaled = 1;
- /*
- * Don't send IPI to itself. With irqs disabled,
- * rdp->cpu is the current cpu.
- */
- cpumask = rcp->cpumask;
- cpu_clear(rdp->cpu, cpumask);
- for_each_cpu_mask(cpu, cpumask)
- smp_send_reschedule(cpu);
- }
-}
-#else
-static inline void force_quiescent_state(struct rcu_data *rdp,
- struct rcu_ctrlblk *rcp)
+/* Because of FASTCALL declaration of complete, we use this wrapper */
+static void wakeme_after_rcu(struct rcu_head *head)
{
- set_need_resched();
+ struct rcu_synchronize *rcu;
+
+ rcu = container_of(head, struct rcu_synchronize, head);
+ complete(&rcu->completion);
}
-#endif
/**
- * call_rcu - Queue an RCU callback for invocation after a grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual update function to be invoked after the grace period
+ * synchronize_rcu - wait until a grace period has elapsed.
*
- * The update function will be invoked some time after a full grace
- * period elapses, in other words after all currently executing RCU
+ * Control will return to the caller some time after a full grace
+ * period has elapsed, in other words after all currently executing RCU
* read-side critical sections have completed. RCU read-side critical
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
* and may be nested.
*/
-void fastcall call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
-{
- unsigned long flags;
- struct rcu_data *rdp;
-
- head->func = func;
- head->next = NULL;
- local_irq_save(flags);
- rdp = &__get_cpu_var(rcu_data);
- *rdp->nxttail = head;
- rdp->nxttail = &head->next;
- if (unlikely(++rdp->qlen > qhimark)) {
- rdp->blimit = INT_MAX;
- force_quiescent_state(rdp, &rcu_ctrlblk);
- }
- local_irq_restore(flags);
-}
-
-/**
- * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
- * @head: structure to be used for queueing the RCU updates.
- * @func: actual update function to be invoked after the grace period
- *
- * The update function will be invoked some time after a full grace
- * period elapses, in other words after all currently executing RCU
- * read-side critical sections have completed. call_rcu_bh() assumes
- * that the read-side critical sections end on completion of a softirq
- * handler. This means that read-side critical sections in process
- * context must not be interrupted by softirqs. This interface is to be
- * used when most of the read-side critical sections are in softirq context.
- * RCU read-side critical sections are delimited by rcu_read_lock() and
- * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
- * and rcu_read_unlock_bh(), if in process context. These may be nested.
- */
-void fastcall call_rcu_bh(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
+void synchronize_rcu(void)
{
- unsigned long flags;
- struct rcu_data *rdp;
-
- head->func = func;
- head->next = NULL;
- local_irq_save(flags);
- rdp = &__get_cpu_var(rcu_bh_data);
- *rdp->nxttail = head;
- rdp->nxttail = &head->next;
-
- if (unlikely(++rdp->qlen > qhimark)) {
- rdp->blimit = INT_MAX;
- force_quiescent_state(rdp, &rcu_bh_ctrlblk);
- }
-
- local_irq_restore(flags);
-}
+ struct rcu_synchronize rcu;
-/*
- * Return the number of RCU batches processed thus far. Useful
- * for debug and statistics.
- */
-long rcu_batches_completed(void)
-{
- return rcu_ctrlblk.completed;
-}
+ init_completion(&rcu.completion);
+ /* Will wake me after RCU finished */
+ call_rcu(&rcu.head, wakeme_after_rcu);
-/*
- * Return the number of RCU batches processed thus far. Useful
- * for debug and statistics.
- */
-long rcu_batches_completed_bh(void)
-{
- return rcu_bh_ctrlblk.completed;
+ /* Wait for it */
+ wait_for_completion(&rcu.completion);
}
static void rcu_barrier_callback(struct rcu_head *notused)
@@ -200,10 +99,8 @@ static void rcu_barrier_callback(struct
static void rcu_barrier_func(void *notused)
{
int cpu = smp_processor_id();
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- struct rcu_head *head;
+ struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
- head = &rdp->barrier;
atomic_inc(&rcu_barrier_cpu_count);
call_rcu(head, rcu_barrier_callback);
}
@@ -222,416 +119,11 @@ void rcu_barrier(void)
wait_for_completion(&rcu_barrier_completion);
mutex_unlock(&rcu_barrier_mutex);
}
-EXPORT_SYMBOL_GPL(rcu_barrier);
-
-/*
- * Invoke the completed RCU callbacks. They are expected to be in
- * a per-cpu list.
- */
-static void rcu_do_batch(struct rcu_data *rdp)
-{
- struct rcu_head *next, *list;
- int count = 0;
-
- list = rdp->donelist;
- while (list) {
- next = list->next;
- prefetch(next);
- list->func(list);
- list = next;
- if (++count >= rdp->blimit)
- break;
- }
- rdp->donelist = list;
-
- local_irq_disable();
- rdp->qlen -= count;
- local_irq_enable();
- if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
- rdp->blimit = blimit;
-
- if (!rdp->donelist)
- rdp->donetail = &rdp->donelist;
- else
- tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
-}
-
-/*
- * Grace period handling:
- * The grace period handling consists out of two steps:
- * - A new grace period is started.
- * This is done by rcu_start_batch. The start is not broadcasted to
- * all cpus, they must pick this up by comparing rcp->cur with
- * rdp->quiescbatch. All cpus are recorded in the
- * rcu_ctrlblk.cpumask bitmap.
- * - All cpus must go through a quiescent state.
- * Since the start of the grace period is not broadcasted, at least two
- * calls to rcu_check_quiescent_state are required:
- * The first call just notices that a new grace period is running. The
- * following calls check if there was a quiescent state since the beginning
- * of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
- * the bitmap is empty, then the grace period is completed.
- * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
- * period (if necessary).
- */
-/*
- * Register a new batch of callbacks, and start it up if there is currently no
- * active batch and the batch to be registered has not already occurred.
- * Caller must hold rcu_ctrlblk.lock.
- */
-static void rcu_start_batch(struct rcu_ctrlblk *rcp)
-{
- if (rcp->next_pending &&
- rcp->completed == rcp->cur) {
- rcp->next_pending = 0;
- /*
- * next_pending == 0 must be visible in
- * __rcu_process_callbacks() before it can see new value of cur.
- */
- smp_wmb();
- rcp->cur++;
-
- /*
- * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
- * Barrier Otherwise it can cause tickless idle CPUs to be
- * included in rcp->cpumask, which will extend graceperiods
- * unnecessarily.
- */
- smp_mb();
- cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
-
- rcp->signaled = 0;
- }
-}
-
-/*
- * cpu went through a quiescent state since the beginning of the grace period.
- * Clear it from the cpu mask and complete the grace period if it was the last
- * cpu. Start another grace period if someone has further entries pending
- */
-static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
-{
- cpu_clear(cpu, rcp->cpumask);
- if (cpus_empty(rcp->cpumask)) {
- /* batch completed ! */
- rcp->completed = rcp->cur;
- rcu_start_batch(rcp);
- }
-}
-
-/*
- * Check if the cpu has gone through a quiescent state (say context
- * switch). If so and if it already hasn't done so in this RCU
- * quiescent cycle, then indicate that it has done so.
- */
-static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
- struct rcu_data *rdp)
-{
- if (rdp->quiescbatch != rcp->cur) {
- /* start new grace period: */
- rdp->qs_pending = 1;
- rdp->passed_quiesc = 0;
- rdp->quiescbatch = rcp->cur;
- return;
- }
-
- /* Grace period already completed for this cpu?
- * qs_pending is checked instead of the actual bitmap to avoid
- * cacheline trashing.
- */
- if (!rdp->qs_pending)
- return;
-
- /*
- * Was there a quiescent state since the beginning of the grace
- * period? If no, then exit and wait for the next call.
- */
- if (!rdp->passed_quiesc)
- return;
- rdp->qs_pending = 0;
-
- spin_lock(&rcp->lock);
- /*
- * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
- * during cpu startup. Ignore the quiescent state.
- */
- if (likely(rdp->quiescbatch == rcp->cur))
- cpu_quiet(rdp->cpu, rcp);
-
- spin_unlock(&rcp->lock);
-}
-
-
-#ifdef CONFIG_HOTPLUG_CPU
-
-/* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
- * locking requirements, the list it's pulling from has to belong to a cpu
- * which is dead and hence not processing interrupts.
- */
-static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
- struct rcu_head **tail)
-{
- local_irq_disable();
- *this_rdp->nxttail = list;
- if (list)
- this_rdp->nxttail = tail;
- local_irq_enable();
-}
-
-static void __rcu_offline_cpu(struct rcu_data *this_rdp,
- struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
-{
- /* if the cpu going offline owns the grace period
- * we can block indefinitely waiting for it, so flush
- * it here
- */
- spin_lock_bh(&rcp->lock);
- if (rcp->cur != rcp->completed)
- cpu_quiet(rdp->cpu, rcp);
- spin_unlock_bh(&rcp->lock);
- rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
- rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
- rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
-}
-
-static void rcu_offline_cpu(int cpu)
-{
- struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
- struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
-
- __rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
- &per_cpu(rcu_data, cpu));
- __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
- &per_cpu(rcu_bh_data, cpu));
- put_cpu_var(rcu_data);
- put_cpu_var(rcu_bh_data);
- tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
-}
-#else
-
-static void rcu_offline_cpu(int cpu)
-{
-}
-
-#endif
-
-/*
- * This does the RCU processing work from tasklet context.
- */
-static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
- struct rcu_data *rdp)
-{
- if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
- *rdp->donetail = rdp->curlist;
- rdp->donetail = rdp->curtail;
- rdp->curlist = NULL;
- rdp->curtail = &rdp->curlist;
- }
-
- if (rdp->nxtlist && !rdp->curlist) {
- local_irq_disable();
- rdp->curlist = rdp->nxtlist;
- rdp->curtail = rdp->nxttail;
- rdp->nxtlist = NULL;
- rdp->nxttail = &rdp->nxtlist;
- local_irq_enable();
-
- /*
- * start the next batch of callbacks
- */
-
- /* determine batch number */
- rdp->batch = rcp->cur + 1;
- /* see the comment and corresponding wmb() in
- * the rcu_start_batch()
- */
- smp_rmb();
-
- if (!rcp->next_pending) {
- /* and start it/schedule start if it's a new batch */
- spin_lock(&rcp->lock);
- rcp->next_pending = 1;
- rcu_start_batch(rcp);
- spin_unlock(&rcp->lock);
- }
- }
-
- rcu_check_quiescent_state(rcp, rdp);
- if (rdp->donelist)
- rcu_do_batch(rdp);
-}
-
-static void rcu_process_callbacks(unsigned long unused)
-{
- __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
- __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
-}
-
-static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
-{
- /* This cpu has pending rcu entries and the grace period
- * for them has completed.
- */
- if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
- return 1;
-
- /* This cpu has no pending entries, but there are new entries */
- if (!rdp->curlist && rdp->nxtlist)
- return 1;
-
- /* This cpu has finished callbacks to invoke */
- if (rdp->donelist)
- return 1;
-
- /* The rcu core waits for a quiescent state from the cpu */
- if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
- return 1;
-
- /* nothing to do */
- return 0;
-}
-
-/*
- * Check to see if there is any immediate RCU-related work to be done
- * by the current CPU, returning 1 if so. This function is part of the
- * RCU implementation; it is -not- an exported member of the RCU API.
- */
-int rcu_pending(int cpu)
-{
- return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
- __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
-}
-
-/*
- * Check to see if any future RCU-related work will need to be done
- * by the current CPU, even if none need be done immediately, returning
- * 1 if so. This function is part of the RCU implementation; it is -not-
- * an exported member of the RCU API.
- */
-int rcu_needs_cpu(int cpu)
-{
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
-
- return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
-}
-
-void rcu_check_callbacks(int cpu, int user)
-{
- if (user ||
- (idle_cpu(cpu) && !in_softirq() &&
- hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
- rcu_qsctr_inc(cpu);
- rcu_bh_qsctr_inc(cpu);
- } else if (!in_softirq())
- rcu_bh_qsctr_inc(cpu);
- tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
-}
-
-static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
- struct rcu_data *rdp)
-{
- memset(rdp, 0, sizeof(*rdp));
- rdp->curtail = &rdp->curlist;
- rdp->nxttail = &rdp->nxtlist;
- rdp->donetail = &rdp->donelist;
- rdp->quiescbatch = rcp->completed;
- rdp->qs_pending = 0;
- rdp->cpu = cpu;
- rdp->blimit = blimit;
-}
-
-static void __devinit rcu_online_cpu(int cpu)
-{
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
-
- rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
- rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
- tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
-}
-
-static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
- unsigned long action, void *hcpu)
-{
- long cpu = (long)hcpu;
- switch (action) {
- case CPU_UP_PREPARE:
- case CPU_UP_PREPARE_FROZEN:
- rcu_online_cpu(cpu);
- break;
- case CPU_DEAD:
- case CPU_DEAD_FROZEN:
- rcu_offline_cpu(cpu);
- break;
- default:
- break;
- }
- return NOTIFY_OK;
-}
-
-static struct notifier_block __cpuinitdata rcu_nb = {
- .notifier_call = rcu_cpu_notify,
-};
-
-/*
- * Initializes rcu mechanism. Assumed to be called early.
- * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
- * Note that rcu_qsctr and friends are implicitly
- * initialized due to the choice of ``0'' for RCU_CTR_INVALID.
- */
void __init rcu_init(void)
{
- rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
- (void *)(long)smp_processor_id());
- /* Register notifier for non-boot CPUs */
- register_cpu_notifier(&rcu_nb);
+ __rcu_init();
}
-struct rcu_synchronize {
- struct rcu_head head;
- struct completion completion;
-};
-
-/* Because of FASTCALL declaration of complete, we use this wrapper */
-static void wakeme_after_rcu(struct rcu_head *head)
-{
- struct rcu_synchronize *rcu;
-
- rcu = container_of(head, struct rcu_synchronize, head);
- complete(&rcu->completion);
-}
-
-/**
- * synchronize_rcu - wait until a grace period has elapsed.
- *
- * Control will return to the caller some time after a full grace
- * period has elapsed, in other words after all currently executing RCU
- * read-side critical sections have completed. RCU read-side critical
- * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
- * and may be nested.
- *
- * If your read-side code is not protected by rcu_read_lock(), do -not-
- * use synchronize_rcu().
- */
-void synchronize_rcu(void)
-{
- struct rcu_synchronize rcu;
-
- init_completion(&rcu.completion);
- /* Will wake me after RCU finished */
- call_rcu(&rcu.head, wakeme_after_rcu);
-
- /* Wait for it */
- wait_for_completion(&rcu.completion);
-}
-
-module_param(blimit, int, 0);
-module_param(qhimark, int, 0);
-module_param(qlowmark, int, 0);
-EXPORT_SYMBOL_GPL(rcu_batches_completed);
-EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
-EXPORT_SYMBOL_GPL(call_rcu);
-EXPORT_SYMBOL_GPL(call_rcu_bh);
+EXPORT_SYMBOL_GPL(rcu_barrier);
EXPORT_SYMBOL_GPL(synchronize_rcu);
Fix rcu_barrier() to work properly in preemptive kernel environment.
Also, the ordering of callback must be preserved while moving
callbacks to another CPU during CPU hotplug.
Signed-off-by: Dipankar Sarma <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
---
rcuclassic.c | 2 +-
rcupdate.c | 10 ++++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff -urpNa -X dontdiff linux-2.6.22-a-splitclassic/kernel/rcuclassic.c linux-2.6.22-b-fixbarriers/kernel/rcuclassic.c
--- linux-2.6.22-a-splitclassic/kernel/rcuclassic.c 2007-07-19 15:03:51.000000000 -0700
+++ linux-2.6.22-b-fixbarriers/kernel/rcuclassic.c 2007-07-19 17:10:46.000000000 -0700
@@ -349,9 +349,9 @@ static void __rcu_offline_cpu(struct rcu
if (rcp->cur != rcp->completed)
cpu_quiet(rdp->cpu, rcp);
spin_unlock_bh(&rcp->lock);
+ rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
- rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
}
static void rcu_offline_cpu(int cpu)
diff -urpNa -X dontdiff linux-2.6.22-a-splitclassic/kernel/rcupdate.c linux-2.6.22-b-fixbarriers/kernel/rcupdate.c
--- linux-2.6.22-a-splitclassic/kernel/rcupdate.c 2007-07-19 14:19:03.000000000 -0700
+++ linux-2.6.22-b-fixbarriers/kernel/rcupdate.c 2007-07-19 17:13:31.000000000 -0700
@@ -115,7 +115,17 @@ void rcu_barrier(void)
mutex_lock(&rcu_barrier_mutex);
init_completion(&rcu_barrier_completion);
atomic_set(&rcu_barrier_cpu_count, 0);
+ /*
+ * The queueing of callbacks in all CPUs must be atomic with
+ * respect to RCU, otherwise one CPU may queue a callback,
+ * wait for a grace period, decrement barrier count and call
+ * complete(), while other CPUs have not yet queued anything.
+ * So, we need to make sure that grace periods cannot complete
+ * until all the callbacks are queued.
+ */
+ rcu_read_lock();
on_each_cpu(rcu_barrier_func, NULL, 0, 1);
+ rcu_read_unlock();
wait_for_completion(&rcu_barrier_completion);
mutex_unlock(&rcu_barrier_mutex);
}
This patch implements a new version of RCU which allows its read-side
critical sections to be preempted. It uses a set of counter pairs
to keep track of the read-side critical sections and flips them
when all tasks exit read-side critical section. The details
of this implementation can be found in this paper -
http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf
This patch was developed as a part of the -rt kernel development and
meant to provide better latencies when read-side critical sections of
RCU don't disable preemption. As a consequence of keeping track of RCU
readers, the readers have a slight overhead (optimizations in the paper).
This implementation co-exists with the "classic" RCU implementations
and can be switched to at compiler.
Also includes RCU tracing summarized in debugfs and RCU_SOFTIRQ for
the preemptible variant of RCU.
Signed-off-by: Dipankar Sarma <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]> (for RCU_SOFTIRQ)
Signed-off-by: Paul McKenney <[email protected]>
---
include/linux/interrupt.h | 1
include/linux/rcuclassic.h | 2
include/linux/rcupdate.h | 7
include/linux/rcupreempt.h | 78 +++
include/linux/rcupreempt_trace.h | 100 +++++
include/linux/sched.h | 5
kernel/Kconfig.preempt | 38 +
kernel/Makefile | 7
kernel/fork.c | 4
kernel/rcupreempt.c | 768 +++++++++++++++++++++++++++++++++++++++
kernel/rcupreempt_trace.c | 330 ++++++++++++++++
11 files changed, 1337 insertions(+), 3 deletions(-)
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/include/linux/interrupt.h linux-2.6.22-c-preemptrcu/include/linux/interrupt.h
--- linux-2.6.22-b-fixbarriers/include/linux/interrupt.h 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/include/linux/interrupt.h 2007-07-21 11:16:29.000000000 -0700
@@ -269,6 +269,7 @@ enum
#ifdef CONFIG_HIGH_RES_TIMERS
HRTIMER_SOFTIRQ,
#endif
+ RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */
};
/* softirq mask and active fields moved to irq_cpustat_t in
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/include/linux/rcuclassic.h linux-2.6.22-c-preemptrcu/include/linux/rcuclassic.h
--- linux-2.6.22-b-fixbarriers/include/linux/rcuclassic.h 2007-07-19 14:19:00.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/include/linux/rcuclassic.h 2007-07-21 08:51:53.000000000 -0700
@@ -142,8 +142,6 @@ extern int rcu_needs_cpu(int cpu);
extern void __rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);
extern void rcu_restart_cpu(int cpu);
-extern long rcu_batches_completed(void);
-extern long rcu_batches_completed_bh(void);
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUCLASSIC_H */
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/include/linux/rcupdate.h linux-2.6.22-c-preemptrcu/include/linux/rcupdate.h
--- linux-2.6.22-b-fixbarriers/include/linux/rcupdate.h 2007-07-19 14:02:36.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/include/linux/rcupdate.h 2007-07-21 12:29:29.000000000 -0700
@@ -52,7 +52,11 @@ struct rcu_head {
void (*func)(struct rcu_head *head);
};
+#ifdef CONFIG_CLASSIC_RCU
#include <linux/rcuclassic.h>
+#else /* #ifdef CONFIG_CLASSIC_RCU */
+#include <linux/rcupreempt.h>
+#endif /* #else #ifdef CONFIG_CLASSIC_RCU */
#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
@@ -218,10 +222,13 @@ extern void FASTCALL(call_rcu_bh(struct
/* Exported common interfaces */
extern void synchronize_rcu(void);
extern void rcu_barrier(void);
+extern long rcu_batches_completed(void);
+extern long rcu_batches_completed_bh(void);
/* Internal to kernel */
extern void rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);
+extern int rcu_needs_cpu(int cpu);
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPDATE_H */
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/include/linux/rcupreempt.h linux-2.6.22-c-preemptrcu/include/linux/rcupreempt.h
--- linux-2.6.22-b-fixbarriers/include/linux/rcupreempt.h 1969-12-31 16:00:00.000000000 -0800
+++ linux-2.6.22-c-preemptrcu/include/linux/rcupreempt.h 2007-07-21 15:54:55.000000000 -0700
@@ -0,0 +1,78 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion (RT implementation)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2006
+ *
+ * Author: Paul McKenney <[email protected]>
+ *
+ * Based on the original work by Paul McKenney <[email protected]>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU
+ *
+ */
+
+#ifndef __LINUX_RCUPREEMPT_H
+#define __LINUX_RCUPREEMPT_H
+
+#ifdef __KERNEL__
+
+#include <linux/cache.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+#include <linux/percpu.h>
+#include <linux/cpumask.h>
+#include <linux/seqlock.h>
+
+#define rcu_qsctr_inc(cpu)
+#define rcu_bh_qsctr_inc(cpu)
+#define call_rcu_bh(head, rcu) call_rcu(head, rcu)
+
+extern void __rcu_read_lock(void);
+extern void __rcu_read_unlock(void);
+extern int rcu_pending(int cpu);
+extern int rcu_needs_cpu(int cpu);
+
+#define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
+#define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); }
+
+#define __rcu_read_lock_nesting() (current->rcu_read_lock_nesting)
+
+extern void __synchronize_sched(void);
+
+extern void __rcu_init(void);
+extern void rcu_check_callbacks(int cpu, int user);
+extern void rcu_restart_cpu(int cpu);
+
+#ifdef CONFIG_RCU_TRACE
+struct rcupreempt_trace;
+extern int *rcupreempt_flipctr(int cpu);
+extern long rcupreempt_data_completed(void);
+extern int rcupreempt_flip_flag(int cpu);
+extern int rcupreempt_mb_flag(int cpu);
+extern char *rcupreempt_try_flip_state_name(void);
+extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu);
+#endif
+
+struct softirq_action;
+
+#endif /* __KERNEL__ */
+#endif /* __LINUX_RCUPREEMPT_H */
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/include/linux/rcupreempt_trace.h linux-2.6.22-c-preemptrcu/include/linux/rcupreempt_trace.h
--- linux-2.6.22-b-fixbarriers/include/linux/rcupreempt_trace.h 1969-12-31 16:00:00.000000000 -0800
+++ linux-2.6.22-c-preemptrcu/include/linux/rcupreempt_trace.h 2007-07-21 10:06:02.000000000 -0700
@@ -0,0 +1,100 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion (RT implementation)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2006
+ *
+ * Author: Paul McKenney <[email protected]>
+ *
+ * Based on the original work by Paul McKenney <[email protected]>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * http://lse.sourceforge.net/locking/rcupdate.html
+ *
+ */
+
+#ifndef __LINUX_RCUPREEMPT_TRACE_H
+#define __LINUX_RCUPREEMPT_TRACE_H
+
+#ifdef __KERNEL__
+#include <linux/types.h>
+#include <linux/kernel.h>
+
+#include <asm/atomic.h>
+
+/*
+ * PREEMPT_RCU data structures.
+ */
+
+struct rcupreempt_trace {
+ long next_length;
+ long next_add;
+ long wait_length;
+ long wait_add;
+ long done_length;
+ long done_add;
+ long done_remove;
+ atomic_t done_invoked;
+ long rcu_check_callbacks;
+ atomic_t rcu_try_flip_1;
+ atomic_t rcu_try_flip_e1;
+ long rcu_try_flip_i1;
+ long rcu_try_flip_ie1;
+ long rcu_try_flip_g1;
+ long rcu_try_flip_a1;
+ long rcu_try_flip_ae1;
+ long rcu_try_flip_a2;
+ long rcu_try_flip_z1;
+ long rcu_try_flip_ze1;
+ long rcu_try_flip_z2;
+ long rcu_try_flip_m1;
+ long rcu_try_flip_me1;
+ long rcu_try_flip_m2;
+};
+
+#ifdef CONFIG_RCU_TRACE
+#define RCU_TRACE(fn, arg) fn(arg);
+#else
+#define RCU_TRACE(fn, arg)
+#endif
+
+extern void rcupreempt_trace_move2done(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_move2wait(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_e1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_i1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_ie1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_g1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_a1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_ae1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_a2(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_z1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_ze1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_z2(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_m1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_me1(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_try_flip_m2(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_check_callbacks(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_done_remove(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_invoke(struct rcupreempt_trace *trace);
+extern void rcupreempt_trace_next_add(struct rcupreempt_trace *trace);
+
+#endif /* __KERNEL__ */
+#endif /* __LINUX_RCUPREEMPT_TRACE_H */
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/include/linux/sched.h linux-2.6.22-c-preemptrcu/include/linux/sched.h
--- linux-2.6.22-b-fixbarriers/include/linux/sched.h 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/include/linux/sched.h 2007-07-21 09:12:49.000000000 -0700
@@ -850,6 +850,11 @@ struct task_struct {
cpumask_t cpus_allowed;
unsigned int time_slice, first_time_slice;
+#ifdef CONFIG_PREEMPT_RCU
+ int rcu_read_lock_nesting;
+ int rcu_flipctr_idx;
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
+
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
struct sched_info sched_info;
#endif
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/kernel/fork.c linux-2.6.22-c-preemptrcu/kernel/fork.c
--- linux-2.6.22-b-fixbarriers/kernel/fork.c 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/kernel/fork.c 2007-07-21 09:23:20.000000000 -0700
@@ -1032,6 +1032,10 @@ static struct task_struct *copy_process(
INIT_LIST_HEAD(&p->children);
INIT_LIST_HEAD(&p->sibling);
+#ifdef CONFIG_PREEMPT_RCU
+ p->rcu_read_lock_nesting = 0;
+ p->rcu_flipctr_idx = 0;
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
p->vfork_done = NULL;
spin_lock_init(&p->alloc_lock);
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/kernel/Kconfig.preempt linux-2.6.22-c-preemptrcu/kernel/Kconfig.preempt
--- linux-2.6.22-b-fixbarriers/kernel/Kconfig.preempt 2007-07-08 16:32:17.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/kernel/Kconfig.preempt 2007-07-21 10:11:00.000000000 -0700
@@ -63,3 +63,41 @@ config PREEMPT_BKL
Say Y here if you are building a kernel for a desktop system.
Say N if you are unsure.
+choice
+ prompt "RCU implementation type:"
+ default CLASSIC_RCU
+
+config CLASSIC_RCU
+ bool "Classic RCU"
+ help
+ This option selects the classic RCU implementation that is
+ designed for best read-side performance on non-realtime
+ systems.
+
+ Say Y if you are unsure.
+
+config PREEMPT_RCU
+ bool "Preemptible RCU"
+ depends on PREEMPT
+ help
+ This option reduces the latency of the kernel by making certain
+ RCU sections preemptible. Normally RCU code is non-preemptible, if
+ this option is selected then read-only RCU sections become
+ preemptible. This helps latency, but may expose bugs due to
+ now-naive assumptions about each RCU read-side critical section
+ remaining on a given CPU through its execution.
+
+ Say N if you are unsure.
+
+endchoice
+
+config RCU_TRACE
+ bool "Enable tracing for RCU - currently stats in debugfs"
+ select DEBUG_FS
+ default y
+ help
+ This option provides tracing in RCU which presents stats
+ in debugfs for debugging RCU implementation.
+
+ Say Y here if you want to enable RCU tracing
+ Say N if you are unsure.
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/kernel/Makefile linux-2.6.22-c-preemptrcu/kernel/Makefile
--- linux-2.6.22-b-fixbarriers/kernel/Makefile 2007-07-19 12:16:03.000000000 -0700
+++ linux-2.6.22-c-preemptrcu/kernel/Makefile 2007-07-21 10:50:35.000000000 -0700
@@ -6,7 +6,7 @@ obj-y = sched.o fork.o exec_domain.o
exit.o itimer.o time.o softirq.o resource.o \
sysctl.o capability.o ptrace.o timer.o user.o \
signal.o sys.o kmod.o workqueue.o pid.o \
- rcupdate.o rcuclassic.o extable.o params.o posix-timers.o \
+ rcupdate.o extable.o params.o posix-timers.o \
kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
hrtimer.o rwsem.o latency.o nsproxy.o srcu.o die_notifier.o
@@ -46,6 +46,11 @@ obj-$(CONFIG_DETECT_SOFTLOCKUP) += softl
obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
obj-$(CONFIG_SECCOMP) += seccomp.o
obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
+obj-$(CONFIG_CLASSIC_RCU) += rcuclassic.o
+obj-$(CONFIG_PREEMPT_RCU) += rcupreempt.o
+ifeq ($(CONFIG_PREEMPT_RCU),y)
+obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o
+endif
obj-$(CONFIG_RELAY) += relay.o
obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
obj-$(CONFIG_UTS_NS) += utsname.o
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/kernel/rcupreempt.c linux-2.6.22-c-preemptrcu/kernel/rcupreempt.c
--- linux-2.6.22-b-fixbarriers/kernel/rcupreempt.c 1969-12-31 16:00:00.000000000 -0800
+++ linux-2.6.22-c-preemptrcu/kernel/rcupreempt.c 2007-07-21 15:54:15.000000000 -0700
@@ -0,0 +1,768 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion, realtime implementation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2006
+ *
+ * Authors: Paul E. McKenney <[email protected]>
+ * With thanks to Esben Nielsen, Bill Huey, and Ingo Molnar
+ * for pushing me away from locks and towards counters, and
+ * to Suparna Bhattacharya for pushing me completely away
+ * from atomic instructions on the read side.
+ *
+ * Papers: http://www.rdrop.com/users/paulmck/RCU
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU/ *.txt
+ *
+ */
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <asm/atomic.h>
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <linux/completion.h>
+#include <linux/moduleparam.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/rcupdate.h>
+#include <linux/cpu.h>
+#include <linux/random.h>
+#include <linux/delay.h>
+#include <linux/byteorder/swabb.h>
+#include <linux/cpumask.h>
+#include <linux/rcupreempt_trace.h>
+
+/*
+ * PREEMPT_RCU data structures.
+ */
+
+#define GP_STAGES 4
+struct rcu_data {
+ spinlock_t lock;
+ long completed; /* Number of last completed batch. */
+ int waitlistcount;
+ struct tasklet_struct rcu_tasklet;
+ struct rcu_head *nextlist;
+ struct rcu_head **nexttail;
+ struct rcu_head *waitlist[GP_STAGES];
+ struct rcu_head **waittail[GP_STAGES];
+ struct rcu_head *donelist;
+ struct rcu_head **donetail;
+#ifdef CONFIG_RCU_TRACE
+ struct rcupreempt_trace trace;
+#endif /* #ifdef CONFIG_RCU_TRACE */
+};
+struct rcu_ctrlblk {
+ spinlock_t fliplock;
+ long completed; /* Number of last completed batch. */
+};
+static DEFINE_PER_CPU(struct rcu_data, rcu_data);
+static struct rcu_ctrlblk rcu_ctrlblk = {
+ .fliplock = SPIN_LOCK_UNLOCKED,
+ .completed = 0,
+};
+static DEFINE_PER_CPU(int [2], rcu_flipctr) = { 0, 0 };
+
+/*
+ * States for rcu_try_flip() and friends.
+ */
+
+enum rcu_try_flip_states {
+ rcu_try_flip_idle_state, /* "I" */
+ rcu_try_flip_waitack_state, /* "A" */
+ rcu_try_flip_waitzero_state, /* "Z" */
+ rcu_try_flip_waitmb_state /* "M" */
+};
+static enum rcu_try_flip_states rcu_try_flip_state = rcu_try_flip_idle_state;
+#ifdef CONFIG_RCU_TRACE
+static char *rcu_try_flip_state_names[] =
+ { "idle", "waitack", "waitzero", "waitmb" };
+#endif /* #ifdef CONFIG_RCU_TRACE */
+
+/*
+ * Enum and per-CPU flag to determine when each CPU has seen
+ * the most recent counter flip.
+ */
+
+enum rcu_flip_flag_values {
+ rcu_flip_seen, /* Steady/initial state, last flip seen. */
+ /* Only GP detector can update. */
+ rcu_flipped /* Flip just completed, need confirmation. */
+ /* Only corresponding CPU can update. */
+};
+static DEFINE_PER_CPU(enum rcu_flip_flag_values, rcu_flip_flag) = rcu_flip_seen;
+
+/*
+ * Enum and per-CPU flag to determine when each CPU has executed the
+ * needed memory barrier to fence in memory references from its last RCU
+ * read-side critical section in the just-completed grace period.
+ */
+
+enum rcu_mb_flag_values {
+ rcu_mb_done, /* Steady/initial state, no mb()s required. */
+ /* Only GP detector can update. */
+ rcu_mb_needed /* Flip just completed, need an mb(). */
+ /* Only corresponding CPU can update. */
+};
+static DEFINE_PER_CPU(enum rcu_mb_flag_values, rcu_mb_flag) = rcu_mb_done;
+
+/*
+ * Macro that prevents the compiler from reordering accesses, but does
+ * absolutely -nothing- to prevent CPUs from reordering. This is used
+ * only to mediate communication between mainline code and hardware
+ * interrupt and NMI handlers.
+ */
+#define ORDERED_WRT_IRQ(x) (*(volatile typeof(x) *)&(x))
+
+/*
+ * RCU_DATA_ME: find the current CPU's rcu_data structure.
+ * RCU_DATA_CPU: find the specified CPU's rcu_data structure.
+ */
+#define RCU_DATA_ME() (&__get_cpu_var(rcu_data))
+#define RCU_DATA_CPU(cpu) (&per_cpu(rcu_data, cpu))
+
+/*
+ * Helper macro for tracing when the appropriate rcu_data is not
+ * cached in a local variable, but where the CPU number is so cached.
+ */
+#define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace));
+
+/*
+ * Helper macro for tracing when the appropriate rcu_data is not
+ * cached in a local variable.
+ */
+#define RCU_TRACE_ME(f) RCU_TRACE(f, &(RCU_DATA_ME()->trace));
+
+/*
+ * Helper macro for tracing when the appropriate rcu_data is pointed
+ * to by a local variable.
+ */
+#define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace));
+
+/*
+ * Return the number of RCU batches processed thus far. Useful
+ * for debug and statistics.
+ */
+long rcu_batches_completed(void)
+{
+ return rcu_ctrlblk.completed;
+}
+
+/*
+ * Return the number of RCU batches processed thus far. Useful for debug
+ * and statistics. The _bh variant is identical to straight RCU.
+ */
+long rcu_batches_completed_bh(void)
+{
+ return rcu_ctrlblk.completed;
+}
+
+void __rcu_read_lock(void)
+{
+ int idx;
+ struct task_struct *me = current;
+ int nesting;
+
+ nesting = ORDERED_WRT_IRQ(me->rcu_read_lock_nesting);
+ if (nesting != 0) {
+
+ /* An earlier rcu_read_lock() covers us, just count it. */
+
+ me->rcu_read_lock_nesting = nesting + 1;
+
+ } else {
+ unsigned long oldirq;
+
+ /*
+ * Disable local interrupts to prevent the grace-period
+ * detection state machine from seeing us half-done.
+ * NMIs can still occur, of course, and might themselves
+ * contain rcu_read_lock().
+ */
+
+ local_irq_save(oldirq);
+
+ /*
+ * Outermost nesting of rcu_read_lock(), so increment
+ * the current counter for the current CPU. Use volatile
+ * casts to prevent the compiler from reordering.
+ */
+
+ idx = ORDERED_WRT_IRQ(rcu_ctrlblk.completed) & 0x1;
+ smp_read_barrier_depends(); /* @@@@ might be unneeded */
+ ORDERED_WRT_IRQ(__get_cpu_var(rcu_flipctr)[idx])++;
+
+ /*
+ * Now that the per-CPU counter has been incremented, we
+ * are protected from races with rcu_read_lock() invoked
+ * from NMI handlers on this CPU. We can therefore safely
+ * increment the nesting counter, relieving further NMIs
+ * of the need to increment the per-CPU counter.
+ */
+
+ ORDERED_WRT_IRQ(me->rcu_read_lock_nesting) = nesting + 1;
+
+ /*
+ * Now that we have preventing any NMIs from storing
+ * to the ->rcu_flipctr_idx, we can safely use it to
+ * remember which counter to decrement in the matching
+ * rcu_read_unlock().
+ */
+
+ ORDERED_WRT_IRQ(me->rcu_flipctr_idx) = idx;
+ local_irq_restore(oldirq);
+ }
+}
+
+void __rcu_read_unlock(void)
+{
+ int idx;
+ struct task_struct *me = current;
+ int nesting;
+
+ nesting = ORDERED_WRT_IRQ(me->rcu_read_lock_nesting);
+ if (nesting > 1) {
+
+ /*
+ * We are still protected by the enclosing rcu_read_lock(),
+ * so simply decrement the counter.
+ */
+
+ me->rcu_read_lock_nesting = nesting - 1;
+
+ } else {
+ unsigned long oldirq;
+
+ /*
+ * Disable local interrupts to prevent the grace-period
+ * detection state machine from seeing us half-done.
+ * NMIs can still occur, of course, and might themselves
+ * contain rcu_read_lock() and rcu_read_unlock().
+ */
+
+ local_irq_save(oldirq);
+
+ /*
+ * Outermost nesting of rcu_read_unlock(), so we must
+ * decrement the current counter for the current CPU.
+ * This must be done carefully, because NMIs can
+ * occur at any point in this code, and any rcu_read_lock()
+ * and rcu_read_unlock() pairs in the NMI handlers
+ * must interact non-destructively with this code.
+ * Lots of volatile casts, and -very- careful ordering.
+ *
+ * Changes to this code, including this one, must be
+ * inspected, validated, and tested extremely carefully!!!
+ */
+
+ /*
+ * First, pick up the index. Enforce ordering for
+ * DEC Alpha.
+ */
+
+ idx = ORDERED_WRT_IRQ(me->rcu_flipctr_idx);
+ smp_read_barrier_depends(); /* @@@ Needed??? */
+
+ /*
+ * Now that we have fetched the counter index, it is
+ * safe to decrement the per-task RCU nesting counter.
+ * After this, any interrupts or NMIs will increment and
+ * decrement the per-CPU counters.
+ */
+ ORDERED_WRT_IRQ(me->rcu_read_lock_nesting) = nesting - 1;
+
+ /*
+ * It is now safe to decrement this task's nesting count.
+ * NMIs that occur after this statement will route their
+ * rcu_read_lock() calls through this "else" clause, and
+ * will thus start incrementing the per-CPU coutner on
+ * their own. They will also clobber ->rcu_flipctr_idx,
+ * but that is OK, since we have already fetched it.
+ */
+
+ ORDERED_WRT_IRQ(__get_cpu_var(rcu_flipctr)[idx])--;
+ local_irq_restore(oldirq);
+ }
+}
+
+/*
+ * If a global counter flip has occurred since the last time that we
+ * advanced callbacks, advance them. Hardware interrupts must be
+ * disabled when calling this function.
+ */
+static void __rcu_advance_callbacks(struct rcu_data *rdp)
+{
+ int cpu;
+ int i;
+ int wlc = 0;
+
+ if (rdp->completed != rcu_ctrlblk.completed) {
+ if (rdp->waitlist[GP_STAGES - 1] != NULL) {
+ *rdp->donetail = rdp->waitlist[GP_STAGES - 1];
+ rdp->donetail = rdp->waittail[GP_STAGES - 1];
+ RCU_TRACE_RDP(rcupreempt_trace_move2done, rdp);
+ }
+ for (i = GP_STAGES - 2; i >= 0; i--) {
+ if (rdp->waitlist[i] != NULL) {
+ rdp->waitlist[i + 1] = rdp->waitlist[i];
+ rdp->waittail[i + 1] = rdp->waittail[i];
+ wlc++;
+ } else {
+ rdp->waitlist[i + 1] = NULL;
+ rdp->waittail[i + 1] =
+ &rdp->waitlist[i + 1];
+ }
+ }
+ if (rdp->nextlist != NULL) {
+ rdp->waitlist[0] = rdp->nextlist;
+ rdp->waittail[0] = rdp->nexttail;
+ wlc++;
+ rdp->nextlist = NULL;
+ rdp->nexttail = &rdp->nextlist;
+ RCU_TRACE_RDP(rcupreempt_trace_move2wait, rdp);
+ } else {
+ rdp->waitlist[0] = NULL;
+ rdp->waittail[0] = &rdp->waitlist[0];
+ }
+ rdp->waitlistcount = wlc;
+ rdp->completed = rcu_ctrlblk.completed;
+ }
+
+ /*
+ * Check to see if this CPU needs to report that it has seen
+ * the most recent counter flip, thereby declaring that all
+ * subsequent rcu_read_lock() invocations will respect this flip.
+ */
+
+ cpu = raw_smp_processor_id();
+ if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
+ smp_mb(); /* Subsequent counter accesses must see new value */
+ per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
+ smp_mb(); /* Subsequent RCU read-side critical sections */
+ /* seen -after- acknowledgement. */
+ }
+}
+
+/*
+ * Get here when RCU is idle. Decide whether we need to
+ * move out of idle state, and return non-zero if so.
+ * "Straightforward" approach for the moment, might later
+ * use callback-list lengths, grace-period duration, or
+ * some such to determine when to exit idle state.
+ * Might also need a pre-idle test that does not acquire
+ * the lock, but let's get the simple case working first...
+ */
+
+static int
+rcu_try_flip_idle(void)
+{
+ int cpu;
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_i1);
+ if (!rcu_pending(smp_processor_id())) {
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_ie1);
+ return 0;
+ }
+
+ /*
+ * Do the flip.
+ */
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_g1);
+ rcu_ctrlblk.completed++; /* stands in for rcu_try_flip_g2 */
+
+ /*
+ * Need a memory barrier so that other CPUs see the new
+ * counter value before they see the subsequent change of all
+ * the rcu_flip_flag instances to rcu_flipped.
+ */
+
+ smp_mb();
+
+ /* Now ask each CPU for acknowledgement of the flip. */
+
+ for_each_possible_cpu(cpu)
+ per_cpu(rcu_flip_flag, cpu) = rcu_flipped;
+
+ return 1;
+}
+
+/*
+ * Wait for CPUs to acknowledge the flip.
+ */
+
+static int
+rcu_try_flip_waitack(void)
+{
+ int cpu;
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_a1);
+ for_each_possible_cpu(cpu)
+ if (per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1);
+ return 0;
+ }
+
+ /*
+ * Make sure our checks above don't bleed into subsequent
+ * waiting for the sum of the counters to reach zero.
+ */
+
+ smp_mb();
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_a2);
+ return 1;
+}
+
+/*
+ * Wait for collective ``last'' counter to reach zero,
+ * then tell all CPUs to do an end-of-grace-period memory barrier.
+ */
+
+static int
+rcu_try_flip_waitzero(void)
+{
+ int cpu;
+ int lastidx = !(rcu_ctrlblk.completed & 0x1);
+ int sum = 0;
+
+ /* Check to see if the sum of the "last" counters is zero. */
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_z1);
+ for_each_possible_cpu(cpu)
+ sum += per_cpu(rcu_flipctr, cpu)[lastidx];
+ if (sum != 0) {
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1);
+ return 0;
+ }
+
+ /* Make sure we don't call for memory barriers before we see zero. */
+
+ smp_mb();
+
+ /* Call for a memory barrier from each CPU. */
+
+ for_each_possible_cpu(cpu)
+ per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed;
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_z2);
+ return 1;
+}
+
+/*
+ * Wait for all CPUs to do their end-of-grace-period memory barrier.
+ * Return 0 once all CPUs have done so.
+ */
+
+static int
+rcu_try_flip_waitmb(void)
+{
+ int cpu;
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_m1);
+ for_each_possible_cpu(cpu)
+ if (per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_me1);
+ return 0;
+ }
+
+ smp_mb(); /* Ensure that the above checks precede any following flip. */
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_m2);
+ return 1;
+}
+
+/*
+ * Attempt a single flip of the counters. Remember, a single flip does
+ * -not- constitute a grace period. Instead, the interval between
+ * at least three consecutive flips is a grace period.
+ *
+ * If anyone is nuts enough to run this CONFIG_PREEMPT_RCU implementation
+ * on a large SMP, they might want to use a hierarchical organization of
+ * the per-CPU-counter pairs.
+ */
+static void rcu_try_flip(void)
+{
+ unsigned long oldirq;
+
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_1);
+ if (unlikely(!spin_trylock_irqsave(&rcu_ctrlblk.fliplock, oldirq))) {
+ RCU_TRACE_ME(rcupreempt_trace_try_flip_e1);
+ return;
+ }
+
+ /*
+ * Take the next transition(s) through the RCU grace-period
+ * flip-counter state machine.
+ */
+
+ switch (rcu_try_flip_state) {
+ case rcu_try_flip_idle_state:
+ if (rcu_try_flip_idle())
+ rcu_try_flip_state = rcu_try_flip_waitack_state;
+ break;
+ case rcu_try_flip_waitack_state:
+ if (rcu_try_flip_waitack())
+ rcu_try_flip_state = rcu_try_flip_waitzero_state;
+ break;
+ case rcu_try_flip_waitzero_state:
+ if (rcu_try_flip_waitzero())
+ rcu_try_flip_state = rcu_try_flip_waitmb_state;
+ break;
+ case rcu_try_flip_waitmb_state:
+ if (rcu_try_flip_waitmb())
+ rcu_try_flip_state = rcu_try_flip_idle_state;
+ }
+ spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, oldirq);
+}
+
+/*
+ * Check to see if this CPU needs to do a memory barrier in order to
+ * ensure that any prior RCU read-side critical sections have committed
+ * their counter manipulations and critical-section memory references
+ * before declaring the grace period to be completed.
+ */
+static void rcu_check_mb(int cpu)
+{
+ if (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed) {
+ smp_mb(); /* Ensure RCU read-side accesses are visible. */
+ per_cpu(rcu_mb_flag, cpu) = rcu_mb_done;
+ }
+}
+
+void rcu_check_callbacks(int cpu, int user)
+{
+ unsigned long oldirq;
+ struct rcu_data *rdp = RCU_DATA_CPU(cpu);
+
+ rcu_check_mb(cpu);
+ if (rcu_ctrlblk.completed == rdp->completed) {
+ rcu_try_flip();
+ }
+ spin_lock_irqsave(&rdp->lock, oldirq);
+ RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
+ __rcu_advance_callbacks(rdp);
+ if (rdp->donelist == NULL) {
+ spin_unlock_irqrestore(&rdp->lock, oldirq);
+ } else {
+ spin_unlock_irqrestore(&rdp->lock, oldirq);
+ raise_softirq(RCU_SOFTIRQ);
+ }
+}
+
+/*
+ * Needed by dynticks, to make sure all RCU processing has finished
+ * when we go idle:
+ */
+void rcu_advance_callbacks(int cpu, int user)
+{
+ unsigned long oldirq;
+ struct rcu_data *rdp = RCU_DATA_CPU(cpu);
+
+ if (rcu_ctrlblk.completed == rdp->completed) {
+ rcu_try_flip();
+ if (rcu_ctrlblk.completed == rdp->completed) {
+ return;
+ }
+ }
+ spin_lock_irqsave(&rdp->lock, oldirq);
+ RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
+ __rcu_advance_callbacks(rdp);
+ spin_unlock_irqrestore(&rdp->lock, oldirq);
+}
+
+static void rcu_process_callbacks(struct softirq_action *unused)
+{
+ unsigned long flags;
+ struct rcu_head *next, *list;
+ struct rcu_data *rdp = RCU_DATA_ME();
+
+ spin_lock_irqsave(&rdp->lock, flags);
+ list = rdp->donelist;
+ if (list == NULL) {
+ spin_unlock_irqrestore(&rdp->lock, flags);
+ return;
+ }
+ rdp->donelist = NULL;
+ rdp->donetail = &rdp->donelist;
+ RCU_TRACE_RDP(rcupreempt_trace_done_remove, rdp);
+ spin_unlock_irqrestore(&rdp->lock, flags);
+ while (list) {
+ next = list->next;
+ list->func(list);
+ list = next;
+ RCU_TRACE_ME(rcupreempt_trace_invoke);
+ }
+}
+
+void fastcall call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ unsigned long oldirq;
+ struct rcu_data *rdp;
+
+ head->func = func;
+ head->next = NULL;
+ local_irq_save(oldirq);
+ rdp = RCU_DATA_ME();
+ spin_lock(&rdp->lock);
+ __rcu_advance_callbacks(rdp);
+ *rdp->nexttail = head;
+ rdp->nexttail = &head->next;
+ RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp);
+ spin_unlock(&rdp->lock);
+ local_irq_restore(oldirq);
+}
+
+/*
+ * Wait until all currently running preempt_disable() code segments
+ * (including hardware-irq-disable segments) complete. Note that
+ * in -rt this does -not- necessarily result in all currently executing
+ * interrupt -handlers- having completed.
+ */
+void __synchronize_sched(void)
+{
+ cpumask_t oldmask;
+ int cpu;
+
+ if (sched_getaffinity(0, &oldmask) < 0) {
+ oldmask = cpu_possible_map;
+ }
+ for_each_online_cpu(cpu) {
+ sched_setaffinity(0, cpumask_of_cpu(cpu));
+ schedule();
+ }
+ sched_setaffinity(0, oldmask);
+}
+
+/*
+ * Check to see if any future RCU-related work will need to be done
+ * by the current CPU, even if none need be done immediately, returning
+ * 1 if so. Assumes that notifiers would take care of handling any
+ * outstanding requests from the RCU core.
+ *
+ * This function is part of the RCU implementation; it is -not-
+ * an exported member of the RCU API.
+ */
+int rcu_needs_cpu(int cpu)
+{
+ struct rcu_data *rdp = RCU_DATA_CPU(cpu);
+
+ return (rdp->donelist != NULL ||
+ !!rdp->waitlistcount ||
+ rdp->nextlist != NULL);
+}
+
+int rcu_pending(int cpu)
+{
+ struct rcu_data *rdp = RCU_DATA_CPU(cpu);
+
+ /* The CPU has at least one callback queued somewhere. */
+
+ if (rdp->donelist != NULL ||
+ !!rdp->waitlistcount ||
+ rdp->nextlist != NULL)
+ return 1;
+
+ /* The RCU core needs an acknowledgement from this CPU. */
+
+ if ((per_cpu(rcu_flip_flag, cpu) == rcu_flipped) ||
+ (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed))
+ return 1;
+
+ /* This CPU has fallen behind the global grace-period number. */
+
+ if (rdp->completed != rcu_ctrlblk.completed)
+ return 1;
+
+ /* Nothing needed from this CPU. */
+
+ return 0;
+}
+
+void __init __rcu_init(void)
+{
+ int cpu;
+ int i;
+ struct rcu_data *rdp;
+
+/*&&&&*/printk("WARNING: experimental non-atomic RCU implementation.\n");
+ for_each_possible_cpu(cpu) {
+ rdp = RCU_DATA_CPU(cpu);
+ spin_lock_init(&rdp->lock);
+ rdp->completed = 0;
+ rdp->waitlistcount = 0;
+ rdp->nextlist = NULL;
+ rdp->nexttail = &rdp->nextlist;
+ for (i = 0; i < GP_STAGES; i++) {
+ rdp->waitlist[i] = NULL;
+ rdp->waittail[i] = &rdp->waitlist[i];
+ }
+ rdp->donelist = NULL;
+ rdp->donetail = &rdp->donelist;
+ }
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
+/*&&&&*/printk("experimental non-atomic RCU implementation: init done\n");
+}
+
+/*
+ * Deprecated, use synchronize_rcu() or synchronize_sched() instead.
+ */
+void synchronize_kernel(void)
+{
+ synchronize_rcu();
+}
+
+#ifdef CONFIG_RCU_TRACE
+int *rcupreempt_flipctr(int cpu)
+{
+ return &per_cpu(rcu_flipctr, cpu)[0];
+}
+int rcupreempt_flip_flag(int cpu)
+{
+ return per_cpu(rcu_flip_flag, cpu);
+}
+int rcupreempt_mb_flag(int cpu)
+{
+ return per_cpu(rcu_mb_flag, cpu);
+}
+char *rcupreempt_try_flip_state_name(void)
+{
+ return rcu_try_flip_state_names[rcu_try_flip_state];
+}
+struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu)
+{
+ struct rcu_data *rdp = RCU_DATA_CPU(cpu);
+
+ return &rdp->trace;
+}
+EXPORT_SYMBOL_GPL(rcupreempt_flipctr);
+EXPORT_SYMBOL_GPL(rcupreempt_flip_flag);
+EXPORT_SYMBOL_GPL(rcupreempt_mb_flag);
+EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name);
+#endif /* #ifdef RCU_TRACE */
+
+EXPORT_SYMBOL_GPL(call_rcu);
+EXPORT_SYMBOL_GPL(rcu_batches_completed);
+EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
+EXPORT_SYMBOL_GPL(__synchronize_sched);
+EXPORT_SYMBOL_GPL(__rcu_read_lock);
+EXPORT_SYMBOL_GPL(__rcu_read_unlock);
diff -urpNa -X dontdiff linux-2.6.22-b-fixbarriers/kernel/rcupreempt_trace.c linux-2.6.22-c-preemptrcu/kernel/rcupreempt_trace.c
--- linux-2.6.22-b-fixbarriers/kernel/rcupreempt_trace.c 1969-12-31 16:00:00.000000000 -0800
+++ linux-2.6.22-c-preemptrcu/kernel/rcupreempt_trace.c 2007-07-21 12:26:30.000000000 -0700
@@ -0,0 +1,330 @@
+/*
+ * Read-Copy Update tracing for realtime implementation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright IBM Corporation, 2006
+ *
+ * Papers: http://www.rdrop.com/users/paulmck/RCU
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU/ *.txt
+ *
+ */
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <asm/atomic.h>
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <linux/completion.h>
+#include <linux/moduleparam.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/rcupdate.h>
+#include <linux/cpu.h>
+#include <linux/mutex.h>
+#include <linux/rcupreempt_trace.h>
+#include <linux/debugfs.h>
+
+static struct mutex rcupreempt_trace_mutex;
+static char *rcupreempt_trace_buf;
+#define RCUPREEMPT_TRACE_BUF_SIZE 4096
+
+void rcupreempt_trace_move2done(struct rcupreempt_trace *trace)
+{
+ trace->done_length += trace->wait_length;
+ trace->done_add += trace->wait_length;
+ trace->wait_length = 0;
+}
+void rcupreempt_trace_move2wait(struct rcupreempt_trace *trace)
+{
+ trace->wait_length += trace->next_length;
+ trace->wait_add += trace->next_length;
+ trace->next_length = 0;
+}
+void rcupreempt_trace_try_flip_1(struct rcupreempt_trace *trace)
+{
+ atomic_inc(&trace->rcu_try_flip_1);
+}
+void rcupreempt_trace_try_flip_e1(struct rcupreempt_trace *trace)
+{
+ atomic_inc(&trace->rcu_try_flip_e1);
+}
+void rcupreempt_trace_try_flip_i1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_i1++;
+}
+void rcupreempt_trace_try_flip_ie1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_ie1++;
+}
+void rcupreempt_trace_try_flip_g1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_g1++;
+}
+void rcupreempt_trace_try_flip_a1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_a1++;
+}
+void rcupreempt_trace_try_flip_ae1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_ae1++;
+}
+void rcupreempt_trace_try_flip_a2(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_a2++;
+}
+void rcupreempt_trace_try_flip_z1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_z1++;
+}
+void rcupreempt_trace_try_flip_ze1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_ze1++;
+}
+void rcupreempt_trace_try_flip_z2(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_z2++;
+}
+void rcupreempt_trace_try_flip_m1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_m1++;
+}
+void rcupreempt_trace_try_flip_me1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_me1++;
+}
+void rcupreempt_trace_try_flip_m2(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_m2++;
+}
+void rcupreempt_trace_check_callbacks(struct rcupreempt_trace *trace)
+{
+ trace->rcu_check_callbacks++;
+}
+void rcupreempt_trace_done_remove(struct rcupreempt_trace *trace)
+{
+ trace->done_remove += trace->done_length;
+ trace->done_length = 0;
+}
+void rcupreempt_trace_invoke(struct rcupreempt_trace *trace)
+{
+ atomic_inc(&trace->done_invoked);
+}
+void rcupreempt_trace_next_add(struct rcupreempt_trace *trace)
+{
+ trace->next_add++;
+ trace->next_length++;
+}
+
+static void rcupreempt_trace_sum(struct rcupreempt_trace *sp)
+{
+ struct rcupreempt_trace *cp;
+ int cpu;
+
+ memset(sp, 0, sizeof(*sp));
+ for_each_possible_cpu(cpu) {
+ cp = rcupreempt_trace_cpu(cpu);
+ sp->next_length += cp->next_length;
+ sp->next_add += cp->next_add;
+ sp->wait_length += cp->wait_length;
+ sp->wait_add += cp->wait_add;
+ sp->done_length += cp->done_length;
+ sp->done_add += cp->done_add;
+ sp->done_remove += cp->done_remove;
+ atomic_set(&sp->done_invoked, atomic_read(&cp->done_invoked));
+ sp->rcu_check_callbacks += cp->rcu_check_callbacks;
+ atomic_set(&sp->rcu_try_flip_1,
+ atomic_read(&cp->rcu_try_flip_1));
+ atomic_set(&sp->rcu_try_flip_e1,
+ atomic_read(&cp->rcu_try_flip_e1));
+ sp->rcu_try_flip_i1 += cp->rcu_try_flip_i1;
+ sp->rcu_try_flip_ie1 += cp->rcu_try_flip_ie1;
+ sp->rcu_try_flip_g1 += cp->rcu_try_flip_g1;
+ sp->rcu_try_flip_a1 += cp->rcu_try_flip_a1;
+ sp->rcu_try_flip_ae1 += cp->rcu_try_flip_ae1;
+ sp->rcu_try_flip_a2 += cp->rcu_try_flip_a2;
+ sp->rcu_try_flip_z1 += cp->rcu_try_flip_z1;
+ sp->rcu_try_flip_ze1 += cp->rcu_try_flip_ze1;
+ sp->rcu_try_flip_z2 += cp->rcu_try_flip_z2;
+ sp->rcu_try_flip_m1 += cp->rcu_try_flip_m1;
+ sp->rcu_try_flip_me1 += cp->rcu_try_flip_me1;
+ sp->rcu_try_flip_m2 += cp->rcu_try_flip_m2;
+ }
+}
+
+static ssize_t rcustats_read(struct file *filp, char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ struct rcupreempt_trace trace;
+ ssize_t bcount;
+ int cnt = 0;
+
+ rcupreempt_trace_sum(&trace);
+ mutex_lock(&rcupreempt_trace_mutex);
+ snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "ggp=%ld rcc=%ld\n",
+ rcu_batches_completed(),
+ trace.rcu_check_callbacks);
+ snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "na=%ld nl=%ld wa=%ld wl=%ld da=%ld dl=%ld dr=%ld di=%d\n"
+ "1=%d e1=%d i1=%ld ie1=%ld g1=%ld a1=%ld ae1=%ld a2=%ld\n"
+ "z1=%ld ze1=%ld z2=%ld m1=%ld me1=%ld m2=%ld\n",
+
+ trace.next_add, trace.next_length,
+ trace.wait_add, trace.wait_length,
+ trace.done_add, trace.done_length,
+ trace.done_remove, atomic_read(&trace.done_invoked),
+ atomic_read(&trace.rcu_try_flip_1),
+ atomic_read(&trace.rcu_try_flip_e1),
+ trace.rcu_try_flip_i1, trace.rcu_try_flip_ie1,
+ trace.rcu_try_flip_g1,
+ trace.rcu_try_flip_a1, trace.rcu_try_flip_ae1,
+ trace.rcu_try_flip_a2,
+ trace.rcu_try_flip_z1, trace.rcu_try_flip_ze1,
+ trace.rcu_try_flip_z2,
+ trace.rcu_try_flip_m1, trace.rcu_try_flip_me1,
+ trace.rcu_try_flip_m2);
+ bcount = simple_read_from_buffer(buffer, count, ppos,
+ rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
+ mutex_unlock(&rcupreempt_trace_mutex);
+ return bcount;
+}
+
+static ssize_t rcugp_read(struct file *filp, char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ long oldgp = rcu_batches_completed();
+ ssize_t bcount;
+
+ mutex_lock(&rcupreempt_trace_mutex);
+ synchronize_rcu();
+ snprintf(rcupreempt_trace_buf, RCUPREEMPT_TRACE_BUF_SIZE,
+ "oldggp=%ld newggp=%ld\n", oldgp, rcu_batches_completed());
+ bcount = simple_read_from_buffer(buffer, count, ppos,
+ rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
+ mutex_unlock(&rcupreempt_trace_mutex);
+ return bcount;
+}
+
+static ssize_t rcuctrs_read(struct file *filp, char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ int cnt = 0;
+ int cpu;
+ int f = rcu_batches_completed() & 0x1;
+ ssize_t bcount;
+
+ mutex_lock(&rcupreempt_trace_mutex);
+
+ cnt += snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE,
+ "CPU last cur F M\n");
+ for_each_online_cpu(cpu) {
+ int *flipctr = rcupreempt_flipctr(cpu);
+ cnt += snprintf(&rcupreempt_trace_buf[cnt],
+ RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "%3d %4d %3d %d %d\n",
+ cpu,
+ flipctr[!f],
+ flipctr[f],
+ rcupreempt_flip_flag(cpu),
+ rcupreempt_mb_flag(cpu));
+ }
+ cnt += snprintf(&rcupreempt_trace_buf[cnt],
+ RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "ggp = %ld, state = %s\n",
+ rcu_batches_completed(),
+ rcupreempt_try_flip_state_name());
+ cnt += snprintf(&rcupreempt_trace_buf[cnt],
+ RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "\n");
+ bcount = simple_read_from_buffer(buffer, count, ppos,
+ rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
+ mutex_unlock(&rcupreempt_trace_mutex);
+ return bcount;
+}
+
+static struct file_operations rcustats_fops = {
+ .owner = THIS_MODULE,
+ .read = rcustats_read,
+};
+
+static struct file_operations rcugp_fops = {
+ .owner = THIS_MODULE,
+ .read = rcugp_read,
+};
+
+static struct file_operations rcuctrs_fops = {
+ .owner = THIS_MODULE,
+ .read = rcuctrs_read,
+};
+
+static struct dentry *rcudir, *statdir, *ctrsdir, *gpdir;
+static int rcupreempt_debugfs_init(void)
+{
+ rcudir = debugfs_create_dir("rcu", NULL);
+ if (!rcudir)
+ goto out;
+ statdir = debugfs_create_file("rcustats", 0444, rcudir,
+ NULL, &rcustats_fops);
+ if (!statdir)
+ goto free_out;
+
+ gpdir = debugfs_create_file("rcugp", 0444, rcudir, NULL, &rcugp_fops);
+ if (!gpdir)
+ goto free_out;
+
+ ctrsdir = debugfs_create_file("rcuctrs", 0444, rcudir,
+ NULL, &rcuctrs_fops);
+ if (!ctrsdir)
+ goto free_out;
+ return 0;
+free_out:
+ if (statdir)
+ debugfs_remove(statdir);
+ if (gpdir)
+ debugfs_remove(gpdir);
+ debugfs_remove(rcudir);
+out:
+ return 1;
+}
+
+static int __init rcupreempt_trace_init(void)
+{
+ mutex_init(&rcupreempt_trace_mutex);
+ rcupreempt_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL);
+ if (!rcupreempt_trace_buf)
+ return 1;
+ return rcupreempt_debugfs_init();
+}
+
+static void __exit rcupreempt_trace_cleanup(void)
+{
+ debugfs_remove(statdir);
+ debugfs_remove(gpdir);
+ debugfs_remove(ctrsdir);
+ debugfs_remove(rcudir);
+ kfree(rcupreempt_trace_buf);
+}
+
+
+module_init(rcupreempt_trace_init);
+module_exit(rcupreempt_trace_cleanup);
The combination of CPU hotplug and PREEMPT_RCU has resulted in deadlocks
due to the migration-based implementation of synchronize_sched() in -rt.
This experimental patch maps synchronize_sched() back onto Classic RCU,
eliminating the migration, thus hopefully also eliminating the deadlocks.
It is not clear that this is a good long-term approach, but it will at
least permit people doing CPU hotplug in -rt kernels additional wiggle
room in their design and implementation.
The basic approach is to cause the -rt kernel to incorporate rcuclassic.c
as well as rcupreempt.c, but to #ifdef out the conflicting portions of
rcuclassic.c so that only the code needed to implement synchronize_sched()
remains in a PREEMPT_RT build. Invocations of grace-period detection
from the scheduling-clock interrupt go to rcuclassic.c, which then invokes
the corresponding functions in rcupreempt.c (with _rt suffix added to
keep the linker happy). Also applies the RCU_SOFTIRQ to classic RCU.
The bulk of this patch just moves code around.
If this patch does turn out to be the right approach, the #ifdefs in
kernel/rcuclassic.c might be dealt with. ;-)
Signed-off-by: Steven Rostedt <[email protected]> (for RCU_SOFTIRQ)
Signed-off-by: Paul E. McKenney <[email protected]>
---
include/linux/rcuclassic.h | 78 +++++---------------------------------
include/linux/rcupdate.h | 30 ++++++++++++--
include/linux/rcupreempt.h | 27 ++++++-------
kernel/Makefile | 2
kernel/rcuclassic.c | 92 ++++++++++++++++++++++++++++++++++++---------
kernel/rcupdate.c | 21 +++++++---
kernel/rcupreempt.c | 50 +++++-------------------
7 files changed, 154 insertions(+), 146 deletions(-)
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/include/linux/rcuclassic.h linux-2.6.22-d-schedclassic/include/linux/rcuclassic.h
--- linux-2.6.22-c-preemptrcu/include/linux/rcuclassic.h 2007-07-21 08:51:53.000000000 -0700
+++ linux-2.6.22-d-schedclassic/include/linux/rcuclassic.h 2007-08-06 10:16:16.000000000 -0700
@@ -43,79 +43,19 @@
#include <linux/seqlock.h>
-/* Global control variables for rcupdate callback mechanism. */
-struct rcu_ctrlblk {
- long cur; /* Current batch number. */
- long completed; /* Number of the last completed batch */
- int next_pending; /* Is the next batch already waiting? */
-
- int signaled;
-
- spinlock_t lock ____cacheline_internodealigned_in_smp;
- cpumask_t cpumask; /* CPUs that need to switch in order */
- /* for current batch to proceed. */
-} ____cacheline_internodealigned_in_smp;
-
-/* Is batch a before batch b ? */
-static inline int rcu_batch_before(long a, long b)
-{
- return (a - b) < 0;
-}
-
-/* Is batch a after batch b ? */
-static inline int rcu_batch_after(long a, long b)
-{
- return (a - b) > 0;
-}
-
-/*
- * Per-CPU data for Read-Copy UPdate.
- * nxtlist - new callbacks are added here
- * curlist - current batch for which quiescent cycle started if any
- */
-struct rcu_data {
- /* 1) quiescent state handling : */
- long quiescbatch; /* Batch # for grace period */
- int passed_quiesc; /* User-mode/idle loop etc. */
- int qs_pending; /* core waits for quiesc state */
-
- /* 2) batch handling */
- long batch; /* Batch # for current RCU batch */
- struct rcu_head *nxtlist;
- struct rcu_head **nxttail;
- long qlen; /* # of queued callbacks */
- struct rcu_head *curlist;
- struct rcu_head **curtail;
- struct rcu_head *donelist;
- struct rcu_head **donetail;
- long blimit; /* Upper limit on a processed batch */
- int cpu;
- struct rcu_head barrier;
-};
-
-DECLARE_PER_CPU(struct rcu_data, rcu_data);
-DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
+DECLARE_PER_CPU(int, rcu_data_bh_passed_quiesc);
/*
- * Increment the quiescent state counter.
+ * Increment the bottom-half quiescent state counter.
* The counter is a bit degenerated: We do not need to know
* how many quiescent states passed, just if there was at least
* one since the start of the grace period. Thus just a flag.
*/
-static inline void rcu_qsctr_inc(int cpu)
-{
- struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
- rdp->passed_quiesc = 1;
-}
static inline void rcu_bh_qsctr_inc(int cpu)
{
- struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
- rdp->passed_quiesc = 1;
+ per_cpu(rcu_data_bh_passed_quiesc, cpu) = 1;
}
-extern int rcu_pending(int cpu);
-extern int rcu_needs_cpu(int cpu);
-
#define __rcu_read_lock() \
do { \
preempt_disable(); \
@@ -139,9 +79,15 @@ extern int rcu_needs_cpu(int cpu);
#define __synchronize_sched() synchronize_rcu()
-extern void __rcu_init(void);
-extern void rcu_check_callbacks(int cpu, int user);
-extern void rcu_restart_cpu(int cpu);
+#define rcu_advance_callbacks_rt(cpu, user)
+#define rcu_check_callbacks_rt(cpu, user)
+#define rcu_init_rt()
+#define rcu_needs_cpu_rt(cpu) 0
+#define rcu_pending_rt(cpu) 0
+#define rcu_process_callbacks_rt(unused)
+
+extern void FASTCALL(call_rcu_classic(struct rcu_head *head,
+ void (*func)(struct rcu_head *head)));
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUCLASSIC_H */
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/include/linux/rcupdate.h linux-2.6.22-d-schedclassic/include/linux/rcupdate.h
--- linux-2.6.22-c-preemptrcu/include/linux/rcupdate.h 2007-07-21 12:29:29.000000000 -0700
+++ linux-2.6.22-d-schedclassic/include/linux/rcupdate.h 2007-08-06 11:23:17.000000000 -0700
@@ -197,8 +197,11 @@ struct rcu_head {
* delimited by rcu_read_lock() and rcu_read_unlock(),
* and may be nested.
*/
-extern void FASTCALL(call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *head)));
+#ifdef CONFIG_CLASSIC_RCU
+#define call_rcu(head, func) call_rcu_classic(head, func)
+#else /* #ifdef CONFIG_CLASSIC_RCU */
+#define call_rcu(head, func) call_rcu_preempt(head, func)
+#endif /* #else #ifdef CONFIG_CLASSIC_RCU */
/**
* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
@@ -226,9 +229,28 @@ extern long rcu_batches_completed(void);
extern long rcu_batches_completed_bh(void);
/* Internal to kernel */
-extern void rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);
-extern int rcu_needs_cpu(int cpu);
+extern long rcu_batches_completed(void);
+extern long rcu_batches_completed_bh(void);
+extern void rcu_check_callbacks(int cpu, int user);
+extern void rcu_init(void);
+extern int rcu_needs_cpu(int cpu);
+extern int rcu_pending(int cpu);
+struct softirq_action;
+extern void rcu_restart_cpu(int cpu);
+
+DECLARE_PER_CPU(int, rcu_data_passed_quiesc);
+
+/*
+ * Increment the quiescent state counter.
+ * The counter is a bit degenerated: We do not need to know
+ * how many quiescent states passed, just if there was at least
+ * one since the start of the grace period. Thus just a flag.
+ */
+static inline void rcu_qsctr_inc(int cpu)
+{
+ per_cpu(rcu_data_passed_quiesc, cpu) = 1;
+}
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPDATE_H */
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/include/linux/rcupreempt.h linux-2.6.22-d-schedclassic/include/linux/rcupreempt.h
--- linux-2.6.22-c-preemptrcu/include/linux/rcupreempt.h 2007-07-21 15:54:55.000000000 -0700
+++ linux-2.6.22-d-schedclassic/include/linux/rcupreempt.h 2007-08-06 14:56:00.000000000 -0700
@@ -42,25 +42,26 @@
#include <linux/cpumask.h>
#include <linux/seqlock.h>
-#define rcu_qsctr_inc(cpu)
-#define rcu_bh_qsctr_inc(cpu)
#define call_rcu_bh(head, rcu) call_rcu(head, rcu)
-
-extern void __rcu_read_lock(void);
-extern void __rcu_read_unlock(void);
-extern int rcu_pending(int cpu);
-extern int rcu_needs_cpu(int cpu);
-
+#define rcu_bh_qsctr_inc(cpu)
#define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
#define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); }
-
#define __rcu_read_lock_nesting() (current->rcu_read_lock_nesting)
+extern void FASTCALL(call_rcu_classic(struct rcu_head *head,
+ void (*func)(struct rcu_head *head)));
+extern void FASTCALL(call_rcu_preempt(struct rcu_head *head,
+ void (*func)(struct rcu_head *head)));
+extern void __rcu_read_lock(void);
+extern void __rcu_read_unlock(void);
extern void __synchronize_sched(void);
-
-extern void __rcu_init(void);
-extern void rcu_check_callbacks(int cpu, int user);
-extern void rcu_restart_cpu(int cpu);
+extern void rcu_advance_callbacks_rt(int cpu, int user);
+extern void rcu_check_callbacks_rt(int cpu, int user);
+extern void rcu_init_rt(void);
+extern int rcu_needs_cpu_rt(int cpu);
+extern int rcu_pending_rt(int cpu);
+struct softirq_action;
+extern void rcu_process_callbacks_rt(struct softirq_action *unused);
#ifdef CONFIG_RCU_TRACE
struct rcupreempt_trace;
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/kernel/Makefile linux-2.6.22-d-schedclassic/kernel/Makefile
--- linux-2.6.22-c-preemptrcu/kernel/Makefile 2007-07-21 10:50:35.000000000 -0700
+++ linux-2.6.22-d-schedclassic/kernel/Makefile 2007-08-06 10:26:47.000000000 -0700
@@ -47,7 +47,7 @@ obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
obj-$(CONFIG_SECCOMP) += seccomp.o
obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
obj-$(CONFIG_CLASSIC_RCU) += rcuclassic.o
-obj-$(CONFIG_PREEMPT_RCU) += rcupreempt.o
+obj-$(CONFIG_PREEMPT_RCU) += rcuclassic.o rcupreempt.o
ifeq ($(CONFIG_PREEMPT_RCU),y)
obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o
endif
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/kernel/rcuclassic.c linux-2.6.22-d-schedclassic/kernel/rcuclassic.c
--- linux-2.6.22-c-preemptrcu/kernel/rcuclassic.c 2007-07-19 17:10:46.000000000 -0700
+++ linux-2.6.22-d-schedclassic/kernel/rcuclassic.c 2007-08-06 14:07:26.000000000 -0700
@@ -45,10 +45,53 @@
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
-/* #include <linux/rcupdate.h> @@@ */
#include <linux/cpu.h>
#include <linux/mutex.h>
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+ long cur; /* Current batch number. */
+ long completed; /* Number of the last completed batch */
+ int next_pending; /* Is the next batch already waiting? */
+
+ int signaled;
+
+ spinlock_t lock ____cacheline_internodealigned_in_smp;
+ cpumask_t cpumask; /* CPUs that need to switch in order */
+ /* for current batch to proceed. */
+} ____cacheline_internodealigned_in_smp;
+
+/* Is batch a before batch b ? */
+static inline int rcu_batch_before(long a, long b)
+{
+ return (a - b) < 0;
+}
+
+/*
+ * Per-CPU data for Read-Copy UPdate.
+ * nxtlist - new callbacks are added here
+ * curlist - current batch for which quiescent cycle started if any
+ */
+struct rcu_data {
+ /* 1) quiescent state handling : */
+ long quiescbatch; /* Batch # for grace period */
+ int *passed_quiesc; /* User-mode/idle loop etc. */
+ int qs_pending; /* core waits for quiesc state */
+
+ /* 2) batch handling */
+ long batch; /* Batch # for current RCU batch */
+ struct rcu_head *nxtlist;
+ struct rcu_head **nxttail;
+ long qlen; /* # of queued callbacks */
+ struct rcu_head *curlist;
+ struct rcu_head **curtail;
+ struct rcu_head *donelist;
+ struct rcu_head **donetail;
+ long blimit; /* Upper limit on a processed batch */
+ int cpu;
+};
+
/* Definition for rcupdate control block. */
static struct rcu_ctrlblk rcu_ctrlblk = {
.cur = -300,
@@ -63,11 +106,11 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk
.cpumask = CPU_MASK_NONE,
};
-DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
-DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
+static DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
+static DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
+DEFINE_PER_CPU(int, rcu_data_bh_passed_quiesc);
/* Fake initialization required by compiler */
-static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
static int blimit = 10;
static int qhimark = 10000;
static int qlowmark = 100;
@@ -110,8 +153,8 @@ static inline void force_quiescent_state
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
* and may be nested.
*/
-void fastcall call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
+void fastcall call_rcu_classic(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
{
unsigned long flags;
struct rcu_data *rdp;
@@ -129,6 +172,8 @@ void fastcall call_rcu(struct rcu_head *
local_irq_restore(flags);
}
+#ifdef CONFIG_CLASSIC_RCU
+
/**
* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
* @head: structure to be used for queueing the RCU updates.
@@ -184,6 +229,8 @@ long rcu_batches_completed_bh(void)
return rcu_bh_ctrlblk.completed;
}
+#endif /* #ifdef CONFIG_CLASSIC_RCU */
+
/*
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
@@ -213,7 +260,7 @@ static void rcu_do_batch(struct rcu_data
if (!rdp->donelist)
rdp->donetail = &rdp->donelist;
else
- tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
+ raise_softirq(RCU_SOFTIRQ);
}
/*
@@ -290,7 +337,7 @@ static void rcu_check_quiescent_state(st
if (rdp->quiescbatch != rcp->cur) {
/* start new grace period: */
rdp->qs_pending = 1;
- rdp->passed_quiesc = 0;
+ *rdp->passed_quiesc = 0;
rdp->quiescbatch = rcp->cur;
return;
}
@@ -306,7 +353,7 @@ static void rcu_check_quiescent_state(st
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
- if (!rdp->passed_quiesc)
+ if (!*rdp->passed_quiesc)
return;
rdp->qs_pending = 0;
@@ -365,7 +412,6 @@ static void rcu_offline_cpu(int cpu)
&per_cpu(rcu_bh_data, cpu));
put_cpu_var(rcu_data);
put_cpu_var(rcu_bh_data);
- tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
}
#else
@@ -377,7 +423,7 @@ static void rcu_offline_cpu(int cpu)
#endif
/*
- * This does the RCU processing work from tasklet context.
+ * This does the RCU processing work from softirq context.
*/
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
struct rcu_data *rdp)
@@ -422,10 +468,11 @@ static void __rcu_process_callbacks(stru
rcu_do_batch(rdp);
}
-static void rcu_process_callbacks(unsigned long unused)
+static void rcu_process_callbacks(struct softirq_action *unused)
{
__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
+ rcu_process_callbacks_rt(unused);
}
static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
@@ -460,7 +507,8 @@ static int __rcu_pending(struct rcu_ctrl
int rcu_pending(int cpu)
{
return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
- __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
+ __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)) ||
+ rcu_pending_rt(cpu);
}
/*
@@ -474,7 +522,8 @@ int rcu_needs_cpu(int cpu)
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
- return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
+ return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu) ||
+ rcu_needs_cpu_rt(cpu));
}
void rcu_check_callbacks(int cpu, int user)
@@ -486,7 +535,8 @@ void rcu_check_callbacks(int cpu, int us
rcu_bh_qsctr_inc(cpu);
} else if (!in_softirq())
rcu_bh_qsctr_inc(cpu);
- tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
+ rcu_check_callbacks_rt(cpu, user);
+ raise_softirq(RCU_SOFTIRQ);
}
static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
@@ -508,8 +558,9 @@ static void __devinit rcu_online_cpu(int
struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
+ rdp->passed_quiesc = &per_cpu(rcu_data_passed_quiesc, cpu);
rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
- tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
+ bh_rdp->passed_quiesc = &per_cpu(rcu_data_bh_passed_quiesc, cpu);
}
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
@@ -541,18 +592,23 @@ static struct notifier_block __cpuinitda
* Note that rcu_qsctr and friends are implicitly
* initialized due to the choice of ``0'' for RCU_CTR_INVALID.
*/
-void __init __rcu_init(void)
+void __init rcu_init(void)
{
rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
(void *)(long)smp_processor_id());
/* Register notifier for non-boot CPUs */
register_cpu_notifier(&rcu_nb);
+ rcu_init_rt();
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
}
module_param(blimit, int, 0);
module_param(qhimark, int, 0);
module_param(qlowmark, int, 0);
+
+#ifdef CONFIG_CLASSIC_RCU
EXPORT_SYMBOL_GPL(rcu_batches_completed);
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
-EXPORT_SYMBOL_GPL(call_rcu);
EXPORT_SYMBOL_GPL(call_rcu_bh);
+#endif /* #ifdef CONFIG_CLASSIC_RCU */
+EXPORT_SYMBOL_GPL(call_rcu_classic);
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/kernel/rcupdate.c linux-2.6.22-d-schedclassic/kernel/rcupdate.c
--- linux-2.6.22-c-preemptrcu/kernel/rcupdate.c 2007-07-19 17:13:31.000000000 -0700
+++ linux-2.6.22-d-schedclassic/kernel/rcupdate.c 2007-08-06 10:53:32.000000000 -0700
@@ -52,6 +52,7 @@ struct rcu_synchronize {
struct completion completion;
};
+DEFINE_PER_CPU(int, rcu_data_passed_quiesc);
static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
static atomic_t rcu_barrier_cpu_count;
static DEFINE_MUTEX(rcu_barrier_mutex);
@@ -87,6 +88,21 @@ void synchronize_rcu(void)
wait_for_completion(&rcu.completion);
}
+#ifdef CONFIG_PREEMPT_RCU
+
+/*
+ * Map synchronize_sched() to the classic RCU implementation.
+ */
+void __synchronize_sched(void)
+{
+ struct rcu_synchronize rcu;
+
+ init_completion(&rcu.completion);
+ call_rcu_classic(&rcu.head, wakeme_after_rcu);
+ wait_for_completion(&rcu.completion);
+}
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
+
static void rcu_barrier_callback(struct rcu_head *notused)
{
if (atomic_dec_and_test(&rcu_barrier_cpu_count))
@@ -130,10 +146,5 @@ void rcu_barrier(void)
mutex_unlock(&rcu_barrier_mutex);
}
-void __init rcu_init(void)
-{
- __rcu_init();
-}
-
EXPORT_SYMBOL_GPL(rcu_barrier);
EXPORT_SYMBOL_GPL(synchronize_rcu);
diff -urpNa -X dontdiff linux-2.6.22-c-preemptrcu/kernel/rcupreempt.c linux-2.6.22-d-schedclassic/kernel/rcupreempt.c
--- linux-2.6.22-c-preemptrcu/kernel/rcupreempt.c 2007-07-21 15:54:15.000000000 -0700
+++ linux-2.6.22-d-schedclassic/kernel/rcupreempt.c 2007-08-06 14:58:07.000000000 -0700
@@ -61,7 +61,6 @@ struct rcu_data {
spinlock_t lock;
long completed; /* Number of last completed batch. */
int waitlistcount;
- struct tasklet_struct rcu_tasklet;
struct rcu_head *nextlist;
struct rcu_head **nexttail;
struct rcu_head *waitlist[GP_STAGES];
@@ -548,7 +547,7 @@ static void rcu_check_mb(int cpu)
}
}
-void rcu_check_callbacks(int cpu, int user)
+void rcu_check_callbacks_rt(int cpu, int user)
{
unsigned long oldirq;
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
@@ -560,19 +559,14 @@ void rcu_check_callbacks(int cpu, int us
spin_lock_irqsave(&rdp->lock, oldirq);
RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
__rcu_advance_callbacks(rdp);
- if (rdp->donelist == NULL) {
- spin_unlock_irqrestore(&rdp->lock, oldirq);
- } else {
- spin_unlock_irqrestore(&rdp->lock, oldirq);
- raise_softirq(RCU_SOFTIRQ);
- }
+ spin_unlock_irqrestore(&rdp->lock, oldirq);
}
/*
* Needed by dynticks, to make sure all RCU processing has finished
- * when we go idle:
+ * when we go idle. (Currently unused, needed?)
*/
-void rcu_advance_callbacks(int cpu, int user)
+void rcu_advance_callbacks_rt(int cpu, int user)
{
unsigned long oldirq;
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
@@ -589,7 +583,7 @@ void rcu_advance_callbacks(int cpu, int
spin_unlock_irqrestore(&rdp->lock, oldirq);
}
-static void rcu_process_callbacks(struct softirq_action *unused)
+void rcu_process_callbacks_rt(struct softirq_action *unused)
{
unsigned long flags;
struct rcu_head *next, *list;
@@ -613,8 +607,8 @@ static void rcu_process_callbacks(struct
}
}
-void fastcall call_rcu(struct rcu_head *head,
- void (*func)(struct rcu_head *rcu))
+void fastcall call_rcu_preempt(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
{
unsigned long oldirq;
struct rcu_data *rdp;
@@ -633,27 +627,6 @@ void fastcall call_rcu(struct rcu_head *
}
/*
- * Wait until all currently running preempt_disable() code segments
- * (including hardware-irq-disable segments) complete. Note that
- * in -rt this does -not- necessarily result in all currently executing
- * interrupt -handlers- having completed.
- */
-void __synchronize_sched(void)
-{
- cpumask_t oldmask;
- int cpu;
-
- if (sched_getaffinity(0, &oldmask) < 0) {
- oldmask = cpu_possible_map;
- }
- for_each_online_cpu(cpu) {
- sched_setaffinity(0, cpumask_of_cpu(cpu));
- schedule();
- }
- sched_setaffinity(0, oldmask);
-}
-
-/*
* Check to see if any future RCU-related work will need to be done
* by the current CPU, even if none need be done immediately, returning
* 1 if so. Assumes that notifiers would take care of handling any
@@ -662,7 +635,7 @@ void __synchronize_sched(void)
* This function is part of the RCU implementation; it is -not-
* an exported member of the RCU API.
*/
-int rcu_needs_cpu(int cpu)
+int rcu_needs_cpu_rt(int cpu)
{
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
@@ -671,7 +644,7 @@ int rcu_needs_cpu(int cpu)
rdp->nextlist != NULL);
}
-int rcu_pending(int cpu)
+int rcu_pending_rt(int cpu)
{
struct rcu_data *rdp = RCU_DATA_CPU(cpu);
@@ -698,7 +671,7 @@ int rcu_pending(int cpu)
return 0;
}
-void __init __rcu_init(void)
+void __init rcu_init_rt(void)
{
int cpu;
int i;
@@ -719,7 +692,6 @@ void __init __rcu_init(void)
rdp->donelist = NULL;
rdp->donetail = &rdp->donelist;
}
- open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
/*&&&&*/printk("experimental non-atomic RCU implementation: init done\n");
}
@@ -760,7 +732,7 @@ EXPORT_SYMBOL_GPL(rcupreempt_mb_flag);
EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name);
#endif /* #ifdef RCU_TRACE */
-EXPORT_SYMBOL_GPL(call_rcu);
+EXPORT_SYMBOL_GPL(call_rcu_preempt);
EXPORT_SYMBOL_GPL(rcu_batches_completed);
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
EXPORT_SYMBOL_GPL(__synchronize_sched);
On Tue, Aug 07, 2007 at 11:52:26AM -0700, Paul E. McKenney wrote:
> The combination of CPU hotplug and PREEMPT_RCU has resulted in deadlocks
> due to the migration-based implementation of synchronize_sched() in -rt.
> This experimental patch maps synchronize_sched() back onto Classic RCU,
> eliminating the migration, thus hopefully also eliminating the deadlocks.
> It is not clear that this is a good long-term approach, but it will at
> least permit people doing CPU hotplug in -rt kernels additional wiggle
> room in their design and implementation.
>
> The basic approach is to cause the -rt kernel to incorporate rcuclassic.c
> as well as rcupreempt.c, but to #ifdef out the conflicting portions of
> rcuclassic.c so that only the code needed to implement synchronize_sched()
> remains in a PREEMPT_RT build. Invocations of grace-period detection
> from the scheduling-clock interrupt go to rcuclassic.c, which then invokes
> the corresponding functions in rcupreempt.c (with _rt suffix added to
> keep the linker happy). Also applies the RCU_SOFTIRQ to classic RCU.
> The bulk of this patch just moves code around.
>
> If this patch does turn out to be the right approach, the #ifdefs in
> kernel/rcuclassic.c might be dealt with. ;-)
I think the right thing to do would be to fix cpu hotplug to
use a simple reference count, as the latest patches Gautham
is working on. That simplifies the implementation from the
earlier version with a per-cpu reference counter with RCU.
No freezer, no lock.
Thanks
Dipankar
On Tue, 2007-08-07 at 11:48 -0700, Paul E. McKenney wrote:
> This patch implements a new version of RCU which allows its read-side
> critical sections to be preempted. It uses a set of counter pairs
> to keep track of the read-side critical sections and flips them
> when all tasks exit read-side critical section. The details
> of this implementation can be found in this paper -
>
> http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf
>
> This patch was developed as a part of the -rt kernel development and
> meant to provide better latencies when read-side critical sections of
> RCU don't disable preemption. As a consequence of keeping track of RCU
> readers, the readers have a slight overhead (optimizations in the paper).
> This implementation co-exists with the "classic" RCU implementations
> and can be switched to at compiler.
>
> Also includes RCU tracing summarized in debugfs and RCU_SOFTIRQ for
> the preemptible variant of RCU.
Whickedly complex but very cool stuff!
Unfortunately I have nothing to contribute other than praise at the
complex yet elegant way you dodged the need for synchronisation.
On Wed, Aug 08, 2007 at 12:44:30AM +0530, Dipankar Sarma wrote:
> On Tue, Aug 07, 2007 at 11:52:26AM -0700, Paul E. McKenney wrote:
> > The combination of CPU hotplug and PREEMPT_RCU has resulted in deadlocks
> > due to the migration-based implementation of synchronize_sched() in -rt.
> > This experimental patch maps synchronize_sched() back onto Classic RCU,
> > eliminating the migration, thus hopefully also eliminating the deadlocks.
> > It is not clear that this is a good long-term approach, but it will at
> > least permit people doing CPU hotplug in -rt kernels additional wiggle
> > room in their design and implementation.
> >
> > The basic approach is to cause the -rt kernel to incorporate rcuclassic.c
> > as well as rcupreempt.c, but to #ifdef out the conflicting portions of
> > rcuclassic.c so that only the code needed to implement synchronize_sched()
> > remains in a PREEMPT_RT build. Invocations of grace-period detection
> > from the scheduling-clock interrupt go to rcuclassic.c, which then invokes
> > the corresponding functions in rcupreempt.c (with _rt suffix added to
> > keep the linker happy). Also applies the RCU_SOFTIRQ to classic RCU.
> > The bulk of this patch just moves code around.
> >
> > If this patch does turn out to be the right approach, the #ifdefs in
> > kernel/rcuclassic.c might be dealt with. ;-)
>
> I think the right thing to do would be to fix cpu hotplug to
> use a simple reference count, as the latest patches Gautham
> is working on. That simplifies the implementation from the
> earlier version with a per-cpu reference counter with RCU.
> No freezer, no lock.
Works for me -- I will just keep this patch for testing of the
CPU hotplug stuff I am adding to preemptible RCU. Speaking of which,
any advise on good testing methods for CPU hotplug would be greatly
appreciated!!!
Thanx, Paul
On Tue, Aug 07, 2007 at 09:18:29PM +0200, Peter Zijlstra wrote:
> On Tue, 2007-08-07 at 11:48 -0700, Paul E. McKenney wrote:
> > This patch implements a new version of RCU which allows its read-side
> > critical sections to be preempted. It uses a set of counter pairs
> > to keep track of the read-side critical sections and flips them
> > when all tasks exit read-side critical section. The details
> > of this implementation can be found in this paper -
> >
> > http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf
> >
> > This patch was developed as a part of the -rt kernel development and
> > meant to provide better latencies when read-side critical sections of
> > RCU don't disable preemption. As a consequence of keeping track of RCU
> > readers, the readers have a slight overhead (optimizations in the paper).
> > This implementation co-exists with the "classic" RCU implementations
> > and can be switched to at compiler.
> >
> > Also includes RCU tracing summarized in debugfs and RCU_SOFTIRQ for
> > the preemptible variant of RCU.
>
> Whickedly complex but very cool stuff!
>
> Unfortunately I have nothing to contribute other than praise at the
> complex yet elegant way you dodged the need for synchronisation.
I am glad you like it! Heck, I may have to print this email out,
frame it, and hang it on my cube wall. ;-)
Thanx, Paul