This patchset banishes RCU kthreads from non-RCU_BOOST kernel threads.
The two patches are as follows:
1. Minimal patch that #ifdefs out the kthread code.
2. Code-movement patch that puts the code #ifdefed out above
under existing #ifdefs in kernel/rcutree_plugin.h.
For a testing-only version of this patchset from git, please see the
following subject-to-rebase branch:
git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/urgent
Thanx, Paul
------------------------------------------------------------------------
b/kernel/rcutree.c | 59 +++++--
b/kernel/rcutree.h | 8
b/kernel/rcutree_plugin.h | 41 +++-
b/kernel/rcutree_trace.c | 32 ++-
kernel/rcutree.c | 383 ---------------------------------------------
kernel/rcutree.h | 5
kernel/rcutree_plugin.h | 384 ++++++++++++++++++++++++++++++++++++++++++++++
7 files changed, 489 insertions(+), 423 deletions(-)
This patch #ifdefs RCU kthreads out of the kernel unless RCU_BOOST=y,
thus eliminating context-switch overhead if RCU priority boosting has
not been configured.
Signed-off-by: Paul E. McKenney <[email protected]>
---
kernel/rcutree.c | 59 +++++++++++++++++++++++++++++++++++------------
kernel/rcutree.h | 8 ++++-
kernel/rcutree_plugin.h | 41 ++++++++++++++++++++------------
kernel/rcutree_trace.c | 32 ++++++++++++++++++-------
4 files changed, 99 insertions(+), 41 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ae5c9ea..429d494 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -87,6 +87,8 @@ static struct rcu_state *rcu_state;
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
+#ifdef CONFIG_RCU_BOOST
+
/*
* Control variables for per-CPU and per-rcu_node kthreads. These
* handle all flavors of RCU.
@@ -98,9 +100,11 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
DEFINE_PER_CPU(char, rcu_cpu_has_work);
static char rcu_kthreads_spawnable;
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
-static void invoke_rcu_cpu_kthread(void);
-static void __invoke_rcu_cpu_kthread(void);
+static void invoke_rcu_core(void);
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
#define RCU_KTHREAD_PRIO 1 /* RT priority for per-CPU kthreads. */
@@ -1089,6 +1093,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp;
+#ifdef CONFIG_RCU_BOOST
struct task_struct *t;
/* Stop the CPU's kthread. */
@@ -1097,6 +1102,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
kthread_stop(t);
}
+#endif /* #ifdef CONFIG_RCU_BOOST */
/* Exclude any attempts to start a new grace period. */
raw_spin_lock_irqsave(&rsp->onofflock, flags);
@@ -1232,7 +1238,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
/* Re-raise the RCU softirq if there are callbacks remaining. */
if (cpu_has_callbacks_ready_to_invoke(rdp))
- invoke_rcu_cpu_kthread();
+ invoke_rcu_core();
}
/*
@@ -1278,7 +1284,7 @@ void rcu_check_callbacks(int cpu, int user)
}
rcu_preempt_check_callbacks(cpu);
if (rcu_pending(cpu))
- invoke_rcu_cpu_kthread();
+ invoke_rcu_core();
}
#ifdef CONFIG_SMP
@@ -1444,9 +1450,11 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
/* If there are callbacks ready, invoke them. */
if (cpu_has_callbacks_ready_to_invoke(rdp))
- __invoke_rcu_cpu_kthread();
+ invoke_rcu_callbacks(rsp, rdp);
}
+#ifdef CONFIG_RCU_BOOST
+
static void rcu_kthread_do_work(void)
{
rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
@@ -1454,6 +1462,8 @@ static void rcu_kthread_do_work(void)
rcu_preempt_do_callbacks();
}
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
/*
* Do softirq processing for the current CPU.
*/
@@ -1474,25 +1484,22 @@ static void rcu_process_callbacks(struct softirq_action *unused)
* the current CPU with interrupts disabled, the rcu_cpu_kthread_task
* cannot disappear out from under us.
*/
-static void __invoke_rcu_cpu_kthread(void)
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
{
- unsigned long flags;
-
- local_irq_save(flags);
- __this_cpu_write(rcu_cpu_has_work, 1);
- if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) {
- local_irq_restore(flags);
+ if (likely(!rsp->boost)) {
+ rcu_do_batch(rsp, rdp);
return;
}
- wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
- local_irq_restore(flags);
+ invoke_rcu_callbacks_kthread();
}
-static void invoke_rcu_cpu_kthread(void)
+static void invoke_rcu_core(void)
{
raise_softirq(RCU_SOFTIRQ);
}
+#ifdef CONFIG_RCU_BOOST
+
/*
* Wake up the specified per-rcu_node-structure kthread.
* Because the per-rcu_node kthreads are immortal, we don't need
@@ -1818,6 +1825,18 @@ static int __init rcu_spawn_kthreads(void)
}
early_initcall(rcu_spawn_kthreads);
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp)
@@ -2224,6 +2243,8 @@ static void __cpuinit rcu_prepare_cpu(int cpu)
rcu_preempt_init_percpu_data(cpu);
}
+#ifdef CONFIG_RCU_BOOST
+
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
@@ -2237,6 +2258,14 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
}
}
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+static void __cpuinit rcu_prepare_kthreads(int cpu)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
/*
* Handle CPU online/offline notification events.
*/
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 0fed6b9..434288c 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -369,6 +369,7 @@ struct rcu_state {
/* period because */
/* force_quiescent_state() */
/* was running. */
+ u8 boost; /* Subject to priority boost. */
unsigned long gpnum; /* Current gp number. */
unsigned long completed; /* # of last completed gp. */
@@ -439,7 +440,6 @@ static void rcu_preempt_offline_cpu(int cpu);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_preempt_check_callbacks(int cpu);
static void rcu_preempt_process_callbacks(void);
-static void rcu_preempt_do_callbacks(void);
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_TREE_PREEMPT_RCU)
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp);
@@ -451,11 +451,15 @@ static void rcu_preempt_send_cbs_to_online(void);
static void __init __rcu_init_preempt(void);
static void rcu_needs_cpu_flush(void);
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
+static void invoke_rcu_callbacks_kthread(void);
+#ifdef CONFIG_RCU_BOOST
+static void rcu_preempt_do_callbacks(void);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
cpumask_var_t cm);
-static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp,
int rnp_index);
+#endif /* #ifdef CONFIG_RCU_BOOST */
#endif /* #ifndef RCU_TREE_NONCORE */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 38d09c5..2772386 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -602,11 +602,15 @@ static void rcu_preempt_process_callbacks(void)
&__get_cpu_var(rcu_preempt_data));
}
+#ifdef CONFIG_RCU_BOOST
+
static void rcu_preempt_do_callbacks(void)
{
rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
}
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
/*
* Queue a preemptible-RCU callback for invocation after a grace period.
*/
@@ -1002,10 +1006,6 @@ static void rcu_preempt_process_callbacks(void)
{
}
-static void rcu_preempt_do_callbacks(void)
-{
-}
-
/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
* But because preemptible RCU does not exist, map to rcu-sched.
@@ -1258,6 +1258,23 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
}
/*
+ * Wake up the per-CPU kthread to invoke RCU callbacks.
+ */
+static void invoke_rcu_callbacks_kthread(void)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __this_cpu_write(rcu_cpu_has_work, 1);
+ if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) {
+ local_irq_restore(flags);
+ return;
+ }
+ wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
+ local_irq_restore(flags);
+}
+
+/*
* Set the affinity of the boost kthread. The CPU-hotplug locks are
* held, so no one should be messing with the existence of the boost
* kthread.
@@ -1297,6 +1314,7 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
if (&rcu_preempt_state != rsp)
return 0;
+ rsp->boost = 1;
if (rnp->boost_kthread_task != NULL)
return 0;
t = kthread_create(rcu_boost_kthread, (void *)rnp,
@@ -1319,22 +1337,15 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
- cpumask_var_t cm)
+static void invoke_rcu_callbacks_kthread(void)
{
+ WARN_ON_ONCE(1);
}
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}
-static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
- struct rcu_node *rnp,
- int rnp_index)
-{
- return 0;
-}
-
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifndef CONFIG_SMP
@@ -1509,7 +1520,7 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
*
* Because it is not legal to invoke rcu_process_callbacks() with irqs
* disabled, we do one pass of force_quiescent_state(), then do a
- * invoke_rcu_cpu_kthread() to cause rcu_process_callbacks() to be invoked
+ * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
* later. The per-cpu rcu_dyntick_drain variable controls the sequencing.
*/
int rcu_needs_cpu(int cpu)
@@ -1560,7 +1571,7 @@ int rcu_needs_cpu(int cpu)
/* If RCU callbacks are still pending, RCU still needs this CPU. */
if (c)
- invoke_rcu_cpu_kthread();
+ invoke_rcu_core();
return c;
}
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 9678cc3..4e14487 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -46,6 +46,8 @@
#define RCU_TREE_NONCORE
#include "rcutree.h"
+#ifdef CONFIG_RCU_BOOST
+
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_cpu);
DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
@@ -58,6 +60,8 @@ static char convert_kthread_status(unsigned int kthread_status)
return "SRWOY"[kthread_status];
}
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
{
if (!rdp->beenonline)
@@ -76,7 +80,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
- seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c/%d ktl=%x b=%ld",
+ seq_printf(m, " ql=%ld qs=%c%c%c%c",
rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
@@ -84,13 +88,16 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->nxttail[RCU_NEXT_READY_TAIL]],
".W"[rdp->nxttail[RCU_DONE_TAIL] !=
rdp->nxttail[RCU_WAIT_TAIL]],
- ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+ ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+#ifdef CONFIG_RCU_BOOST
+ seq_printf(m, " kt=%d/%c/%d ktl=%x",
per_cpu(rcu_cpu_has_work, rdp->cpu),
convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
rdp->cpu)),
per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
- per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff,
- rdp->blimit);
+ per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ seq_printf(m, " b=%ld", rdp->blimit);
seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
}
@@ -147,18 +154,21 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks_fqs);
#endif /* #ifdef CONFIG_NO_HZ */
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
- seq_printf(m, ",%ld,\"%c%c%c%c\",%d,\"%c\",%ld", rdp->qlen,
+ seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
rdp->nxttail[RCU_NEXT_READY_TAIL]],
".W"[rdp->nxttail[RCU_DONE_TAIL] !=
rdp->nxttail[RCU_WAIT_TAIL]],
- ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+ ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+#ifdef CONFIG_RCU_BOOST
+ seq_printf(m, ",%d,\"%c\"",
per_cpu(rcu_cpu_has_work, rdp->cpu),
convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
- rdp->cpu)),
- rdp->blimit);
+ rdp->cpu)));
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ seq_printf(m, ",%ld", rdp->blimit);
seq_printf(m, ",%lu,%lu,%lu\n",
rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
}
@@ -169,7 +179,11 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
#ifdef CONFIG_NO_HZ
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
#endif /* #ifdef CONFIG_NO_HZ */
- seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\",\"ci\",\"co\",\"ca\"\n");
+ seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
+#ifdef CONFIG_RCU_BOOST
+ seq_puts(m, "\"kt\",\"ktl\"");
+#endif /* #ifdef CONFIG_RCU_BOOST */
+ seq_puts(m, ",\"b\",\"ci\",\"co\",\"ca\"\n");
#ifdef CONFIG_TREE_PREEMPT_RCU
seq_puts(m, "\"rcu_preempt:\"\n");
PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data_csv, m);
--
1.7.3.2
From: Paul E. McKenney <[email protected]>
The commit "use softirq instead of kthreads except when RCU_BOOST=y"
just applied #ifdef in place. This commit is a cleanup that moves
the newly #ifdef'ed code to the header file kernel/rcutree_plugin.h.
Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
---
kernel/rcutree.c | 383 +----------------------------------------------
kernel/rcutree.h | 5 +
kernel/rcutree_plugin.h | 384 +++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 390 insertions(+), 382 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 429d494..7e59ffb 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1093,16 +1093,8 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
int need_report = 0;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp;
-#ifdef CONFIG_RCU_BOOST
- struct task_struct *t;
- /* Stop the CPU's kthread. */
- t = per_cpu(rcu_cpu_kthread_task, cpu);
- if (t != NULL) {
- per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
- kthread_stop(t);
- }
-#endif /* #ifdef CONFIG_RCU_BOOST */
+ rcu_stop_cpu_kthread(cpu);
/* Exclude any attempts to start a new grace period. */
raw_spin_lock_irqsave(&rsp->onofflock, flags);
@@ -1453,17 +1445,6 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
invoke_rcu_callbacks(rsp, rdp);
}
-#ifdef CONFIG_RCU_BOOST
-
-static void rcu_kthread_do_work(void)
-{
- rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
- rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
- rcu_preempt_do_callbacks();
-}
-
-#endif /* #ifdef CONFIG_RCU_BOOST */
-
/*
* Do softirq processing for the current CPU.
*/
@@ -1498,345 +1479,6 @@ static void invoke_rcu_core(void)
raise_softirq(RCU_SOFTIRQ);
}
-#ifdef CONFIG_RCU_BOOST
-
-/*
- * Wake up the specified per-rcu_node-structure kthread.
- * Because the per-rcu_node kthreads are immortal, we don't need
- * to do anything to keep them alive.
- */
-static void invoke_rcu_node_kthread(struct rcu_node *rnp)
-{
- struct task_struct *t;
-
- t = rnp->node_kthread_task;
- if (t != NULL)
- wake_up_process(t);
-}
-
-/*
- * Set the specified CPU's kthread to run RT or not, as specified by
- * the to_rt argument. The CPU-hotplug locks are held, so the task
- * is not going away.
- */
-static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
-{
- int policy;
- struct sched_param sp;
- struct task_struct *t;
-
- t = per_cpu(rcu_cpu_kthread_task, cpu);
- if (t == NULL)
- return;
- if (to_rt) {
- policy = SCHED_FIFO;
- sp.sched_priority = RCU_KTHREAD_PRIO;
- } else {
- policy = SCHED_NORMAL;
- sp.sched_priority = 0;
- }
- sched_setscheduler_nocheck(t, policy, &sp);
-}
-
-/*
- * Timer handler to initiate the waking up of per-CPU kthreads that
- * have yielded the CPU due to excess numbers of RCU callbacks.
- * We wake up the per-rcu_node kthread, which in turn will wake up
- * the booster kthread.
- */
-static void rcu_cpu_kthread_timer(unsigned long arg)
-{
- struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
- struct rcu_node *rnp = rdp->mynode;
-
- atomic_or(rdp->grpmask, &rnp->wakemask);
- invoke_rcu_node_kthread(rnp);
-}
-
-/*
- * Drop to non-real-time priority and yield, but only after posting a
- * timer that will cause us to regain our real-time priority if we
- * remain preempted. Either way, we restore our real-time priority
- * before returning.
- */
-static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
-{
- struct sched_param sp;
- struct timer_list yield_timer;
-
- setup_timer_on_stack(&yield_timer, f, arg);
- mod_timer(&yield_timer, jiffies + 2);
- sp.sched_priority = 0;
- sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
- set_user_nice(current, 19);
- schedule();
- sp.sched_priority = RCU_KTHREAD_PRIO;
- sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
- del_timer(&yield_timer);
-}
-
-/*
- * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
- * This can happen while the corresponding CPU is either coming online
- * or going offline. We cannot wait until the CPU is fully online
- * before starting the kthread, because the various notifier functions
- * can wait for RCU grace periods. So we park rcu_cpu_kthread() until
- * the corresponding CPU is online.
- *
- * Return 1 if the kthread needs to stop, 0 otherwise.
- *
- * Caller must disable bh. This function can momentarily enable it.
- */
-static int rcu_cpu_kthread_should_stop(int cpu)
-{
- while (cpu_is_offline(cpu) ||
- !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) ||
- smp_processor_id() != cpu) {
- if (kthread_should_stop())
- return 1;
- per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
- per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
- local_bh_enable();
- schedule_timeout_uninterruptible(1);
- if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)))
- set_cpus_allowed_ptr(current, cpumask_of(cpu));
- local_bh_disable();
- }
- per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
- return 0;
-}
-
-/*
- * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
- * earlier RCU softirq.
- */
-static int rcu_cpu_kthread(void *arg)
-{
- int cpu = (int)(long)arg;
- unsigned long flags;
- int spincnt = 0;
- unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
- char work;
- char *workp = &per_cpu(rcu_cpu_has_work, cpu);
-
- for (;;) {
- *statusp = RCU_KTHREAD_WAITING;
- rcu_wait(*workp != 0 || kthread_should_stop());
- local_bh_disable();
- if (rcu_cpu_kthread_should_stop(cpu)) {
- local_bh_enable();
- break;
- }
- *statusp = RCU_KTHREAD_RUNNING;
- per_cpu(rcu_cpu_kthread_loops, cpu)++;
- local_irq_save(flags);
- work = *workp;
- *workp = 0;
- local_irq_restore(flags);
- if (work)
- rcu_kthread_do_work();
- local_bh_enable();
- if (*workp != 0)
- spincnt++;
- else
- spincnt = 0;
- if (spincnt > 10) {
- *statusp = RCU_KTHREAD_YIELDING;
- rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
- spincnt = 0;
- }
- }
- *statusp = RCU_KTHREAD_STOPPED;
- return 0;
-}
-
-/*
- * Spawn a per-CPU kthread, setting up affinity and priority.
- * Because the CPU hotplug lock is held, no other CPU will be attempting
- * to manipulate rcu_cpu_kthread_task. There might be another CPU
- * attempting to access it during boot, but the locking in kthread_bind()
- * will enforce sufficient ordering.
- *
- * Please note that we cannot simply refuse to wake up the per-CPU
- * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
- * which can result in softlockup complaints if the task ends up being
- * idle for more than a couple of minutes.
- *
- * However, please note also that we cannot bind the per-CPU kthread to its
- * CPU until that CPU is fully online. We also cannot wait until the
- * CPU is fully online before we create its per-CPU kthread, as this would
- * deadlock the system when CPU notifiers tried waiting for grace
- * periods. So we bind the per-CPU kthread to its CPU only if the CPU
- * is online. If its CPU is not yet fully online, then the code in
- * rcu_cpu_kthread() will wait until it is fully online, and then do
- * the binding.
- */
-static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
-{
- struct sched_param sp;
- struct task_struct *t;
-
- if (!rcu_kthreads_spawnable ||
- per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
- return 0;
- t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
- if (IS_ERR(t))
- return PTR_ERR(t);
- if (cpu_online(cpu))
- kthread_bind(t, cpu);
- per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
- WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
- sp.sched_priority = RCU_KTHREAD_PRIO;
- sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
- per_cpu(rcu_cpu_kthread_task, cpu) = t;
- wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
- return 0;
-}
-
-/*
- * Per-rcu_node kthread, which is in charge of waking up the per-CPU
- * kthreads when needed. We ignore requests to wake up kthreads
- * for offline CPUs, which is OK because force_quiescent_state()
- * takes care of this case.
- */
-static int rcu_node_kthread(void *arg)
-{
- int cpu;
- unsigned long flags;
- unsigned long mask;
- struct rcu_node *rnp = (struct rcu_node *)arg;
- struct sched_param sp;
- struct task_struct *t;
-
- for (;;) {
- rnp->node_kthread_status = RCU_KTHREAD_WAITING;
- rcu_wait(atomic_read(&rnp->wakemask) != 0);
- rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
- raw_spin_lock_irqsave(&rnp->lock, flags);
- mask = atomic_xchg(&rnp->wakemask, 0);
- rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
- if ((mask & 0x1) == 0)
- continue;
- preempt_disable();
- t = per_cpu(rcu_cpu_kthread_task, cpu);
- if (!cpu_online(cpu) || t == NULL) {
- preempt_enable();
- continue;
- }
- per_cpu(rcu_cpu_has_work, cpu) = 1;
- sp.sched_priority = RCU_KTHREAD_PRIO;
- sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
- preempt_enable();
- }
- }
- /* NOTREACHED */
- rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
- return 0;
-}
-
-/*
- * Set the per-rcu_node kthread's affinity to cover all CPUs that are
- * served by the rcu_node in question. The CPU hotplug lock is still
- * held, so the value of rnp->qsmaskinit will be stable.
- *
- * We don't include outgoingcpu in the affinity set, use -1 if there is
- * no outgoing CPU. If there are no CPUs left in the affinity set,
- * this function allows the kthread to execute on any CPU.
- */
-static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
-{
- cpumask_var_t cm;
- int cpu;
- unsigned long mask = rnp->qsmaskinit;
-
- if (rnp->node_kthread_task == NULL)
- return;
- if (!alloc_cpumask_var(&cm, GFP_KERNEL))
- return;
- cpumask_clear(cm);
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
- if ((mask & 0x1) && cpu != outgoingcpu)
- cpumask_set_cpu(cpu, cm);
- if (cpumask_weight(cm) == 0) {
- cpumask_setall(cm);
- for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
- cpumask_clear_cpu(cpu, cm);
- WARN_ON_ONCE(cpumask_weight(cm) == 0);
- }
- set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
- rcu_boost_kthread_setaffinity(rnp, cm);
- free_cpumask_var(cm);
-}
-
-/*
- * Spawn a per-rcu_node kthread, setting priority and affinity.
- * Called during boot before online/offline can happen, or, if
- * during runtime, with the main CPU-hotplug locks held. So only
- * one of these can be executing at a time.
- */
-static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
- struct rcu_node *rnp)
-{
- unsigned long flags;
- int rnp_index = rnp - &rsp->node[0];
- struct sched_param sp;
- struct task_struct *t;
-
- if (!rcu_kthreads_spawnable ||
- rnp->qsmaskinit == 0)
- return 0;
- if (rnp->node_kthread_task == NULL) {
- t = kthread_create(rcu_node_kthread, (void *)rnp,
- "rcun%d", rnp_index);
- if (IS_ERR(t))
- return PTR_ERR(t);
- raw_spin_lock_irqsave(&rnp->lock, flags);
- rnp->node_kthread_task = t;
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
- sp.sched_priority = 99;
- sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
- wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
- }
- return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
-}
-
-/*
- * Spawn all kthreads -- called as soon as the scheduler is running.
- */
-static int __init rcu_spawn_kthreads(void)
-{
- int cpu;
- struct rcu_node *rnp;
-
- rcu_kthreads_spawnable = 1;
- for_each_possible_cpu(cpu) {
- per_cpu(rcu_cpu_has_work, cpu) = 0;
- if (cpu_online(cpu))
- (void)rcu_spawn_one_cpu_kthread(cpu);
- }
- rnp = rcu_get_root(rcu_state);
- (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
- if (NUM_RCU_NODES > 1) {
- rcu_for_each_leaf_node(rcu_state, rnp)
- (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
- }
- return 0;
-}
-early_initcall(rcu_spawn_kthreads);
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
-{
-}
-
-static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
-{
-}
-
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
-
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp)
@@ -2243,29 +1885,6 @@ static void __cpuinit rcu_prepare_cpu(int cpu)
rcu_preempt_init_percpu_data(cpu);
}
-#ifdef CONFIG_RCU_BOOST
-
-static void __cpuinit rcu_prepare_kthreads(int cpu)
-{
- struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
- struct rcu_node *rnp = rdp->mynode;
-
- /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
- if (rcu_kthreads_spawnable) {
- (void)rcu_spawn_one_cpu_kthread(cpu);
- if (rnp->node_kthread_task == NULL)
- (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
- }
-}
-
-#else /* #ifdef CONFIG_RCU_BOOST */
-
-static void __cpuinit rcu_prepare_kthreads(int cpu)
-{
-}
-
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
-
/*
* Handle CPU online/offline notification events.
*/
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 434288c..01b2ccd 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -427,6 +427,7 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
unsigned long flags);
+static void rcu_stop_cpu_kthread(int cpu);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static void rcu_print_detail_task_stall(struct rcu_state *rsp);
static void rcu_print_task_stall(struct rcu_node *rnp);
@@ -460,6 +461,10 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
struct rcu_node *rnp,
int rnp_index);
+static void invoke_rcu_node_kthread(struct rcu_node *rnp);
+static void rcu_yield(void (*f)(unsigned long), unsigned long arg);
#endif /* #ifdef CONFIG_RCU_BOOST */
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt);
+static void __cpuinit rcu_prepare_kthreads(int cpu);
#endif /* #ifndef RCU_TREE_NONCORE */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 2772386..14dc7dd 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1330,6 +1330,370 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
return 0;
}
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Stop the RCU's per-CPU kthread when its CPU goes offline,.
+ */
+static void rcu_stop_cpu_kthread(int cpu)
+{
+ struct task_struct *t;
+
+ /* Stop the CPU's kthread. */
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (t != NULL) {
+ per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
+ kthread_stop(t);
+ }
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+static void rcu_kthread_do_work(void)
+{
+ rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
+ rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
+ rcu_preempt_do_callbacks();
+}
+
+/*
+ * Wake up the specified per-rcu_node-structure kthread.
+ * Because the per-rcu_node kthreads are immortal, we don't need
+ * to do anything to keep them alive.
+ */
+static void invoke_rcu_node_kthread(struct rcu_node *rnp)
+{
+ struct task_struct *t;
+
+ t = rnp->node_kthread_task;
+ if (t != NULL)
+ wake_up_process(t);
+}
+
+/*
+ * Set the specified CPU's kthread to run RT or not, as specified by
+ * the to_rt argument. The CPU-hotplug locks are held, so the task
+ * is not going away.
+ */
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
+{
+ int policy;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (t == NULL)
+ return;
+ if (to_rt) {
+ policy = SCHED_FIFO;
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ } else {
+ policy = SCHED_NORMAL;
+ sp.sched_priority = 0;
+ }
+ sched_setscheduler_nocheck(t, policy, &sp);
+}
+
+/*
+ * Timer handler to initiate the waking up of per-CPU kthreads that
+ * have yielded the CPU due to excess numbers of RCU callbacks.
+ * We wake up the per-rcu_node kthread, which in turn will wake up
+ * the booster kthread.
+ */
+static void rcu_cpu_kthread_timer(unsigned long arg)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
+ struct rcu_node *rnp = rdp->mynode;
+
+ atomic_or(rdp->grpmask, &rnp->wakemask);
+ invoke_rcu_node_kthread(rnp);
+}
+
+/*
+ * Drop to non-real-time priority and yield, but only after posting a
+ * timer that will cause us to regain our real-time priority if we
+ * remain preempted. Either way, we restore our real-time priority
+ * before returning.
+ */
+static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
+{
+ struct sched_param sp;
+ struct timer_list yield_timer;
+
+ setup_timer_on_stack(&yield_timer, f, arg);
+ mod_timer(&yield_timer, jiffies + 2);
+ sp.sched_priority = 0;
+ sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
+ set_user_nice(current, 19);
+ schedule();
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+ del_timer(&yield_timer);
+}
+
+/*
+ * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
+ * This can happen while the corresponding CPU is either coming online
+ * or going offline. We cannot wait until the CPU is fully online
+ * before starting the kthread, because the various notifier functions
+ * can wait for RCU grace periods. So we park rcu_cpu_kthread() until
+ * the corresponding CPU is online.
+ *
+ * Return 1 if the kthread needs to stop, 0 otherwise.
+ *
+ * Caller must disable bh. This function can momentarily enable it.
+ */
+static int rcu_cpu_kthread_should_stop(int cpu)
+{
+ while (cpu_is_offline(cpu) ||
+ !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) ||
+ smp_processor_id() != cpu) {
+ if (kthread_should_stop())
+ return 1;
+ per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+ per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
+ local_bh_enable();
+ schedule_timeout_uninterruptible(1);
+ if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)))
+ set_cpus_allowed_ptr(current, cpumask_of(cpu));
+ local_bh_disable();
+ }
+ per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
+ return 0;
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
+ * earlier RCU softirq.
+ */
+static int rcu_cpu_kthread(void *arg)
+{
+ int cpu = (int)(long)arg;
+ unsigned long flags;
+ int spincnt = 0;
+ unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
+ char work;
+ char *workp = &per_cpu(rcu_cpu_has_work, cpu);
+
+ for (;;) {
+ *statusp = RCU_KTHREAD_WAITING;
+ rcu_wait(*workp != 0 || kthread_should_stop());
+ local_bh_disable();
+ if (rcu_cpu_kthread_should_stop(cpu)) {
+ local_bh_enable();
+ break;
+ }
+ *statusp = RCU_KTHREAD_RUNNING;
+ per_cpu(rcu_cpu_kthread_loops, cpu)++;
+ local_irq_save(flags);
+ work = *workp;
+ *workp = 0;
+ local_irq_restore(flags);
+ if (work)
+ rcu_kthread_do_work();
+ local_bh_enable();
+ if (*workp != 0)
+ spincnt++;
+ else
+ spincnt = 0;
+ if (spincnt > 10) {
+ *statusp = RCU_KTHREAD_YIELDING;
+ rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
+ spincnt = 0;
+ }
+ }
+ *statusp = RCU_KTHREAD_STOPPED;
+ return 0;
+}
+
+/*
+ * Spawn a per-CPU kthread, setting up affinity and priority.
+ * Because the CPU hotplug lock is held, no other CPU will be attempting
+ * to manipulate rcu_cpu_kthread_task. There might be another CPU
+ * attempting to access it during boot, but the locking in kthread_bind()
+ * will enforce sufficient ordering.
+ *
+ * Please note that we cannot simply refuse to wake up the per-CPU
+ * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
+ * which can result in softlockup complaints if the task ends up being
+ * idle for more than a couple of minutes.
+ *
+ * However, please note also that we cannot bind the per-CPU kthread to its
+ * CPU until that CPU is fully online. We also cannot wait until the
+ * CPU is fully online before we create its per-CPU kthread, as this would
+ * deadlock the system when CPU notifiers tried waiting for grace
+ * periods. So we bind the per-CPU kthread to its CPU only if the CPU
+ * is online. If its CPU is not yet fully online, then the code in
+ * rcu_cpu_kthread() will wait until it is fully online, and then do
+ * the binding.
+ */
+static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
+{
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (!rcu_kthreads_spawnable ||
+ per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
+ return 0;
+ t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ if (cpu_online(cpu))
+ kthread_bind(t, cpu);
+ per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
+ WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ per_cpu(rcu_cpu_kthread_task, cpu) = t;
+ wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
+ return 0;
+}
+
+/*
+ * Per-rcu_node kthread, which is in charge of waking up the per-CPU
+ * kthreads when needed. We ignore requests to wake up kthreads
+ * for offline CPUs, which is OK because force_quiescent_state()
+ * takes care of this case.
+ */
+static int rcu_node_kthread(void *arg)
+{
+ int cpu;
+ unsigned long flags;
+ unsigned long mask;
+ struct rcu_node *rnp = (struct rcu_node *)arg;
+ struct sched_param sp;
+ struct task_struct *t;
+
+ for (;;) {
+ rnp->node_kthread_status = RCU_KTHREAD_WAITING;
+ rcu_wait(atomic_read(&rnp->wakemask) != 0);
+ rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ mask = atomic_xchg(&rnp->wakemask, 0);
+ rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
+ if ((mask & 0x1) == 0)
+ continue;
+ preempt_disable();
+ t = per_cpu(rcu_cpu_kthread_task, cpu);
+ if (!cpu_online(cpu) || t == NULL) {
+ preempt_enable();
+ continue;
+ }
+ per_cpu(rcu_cpu_has_work, cpu) = 1;
+ sp.sched_priority = RCU_KTHREAD_PRIO;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ preempt_enable();
+ }
+ }
+ /* NOTREACHED */
+ rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
+ return 0;
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question. The CPU hotplug lock is still
+ * held, so the value of rnp->qsmaskinit will be stable.
+ *
+ * We don't include outgoingcpu in the affinity set, use -1 if there is
+ * no outgoing CPU. If there are no CPUs left in the affinity set,
+ * this function allows the kthread to execute on any CPU.
+ */
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+ cpumask_var_t cm;
+ int cpu;
+ unsigned long mask = rnp->qsmaskinit;
+
+ if (rnp->node_kthread_task == NULL)
+ return;
+ if (!alloc_cpumask_var(&cm, GFP_KERNEL))
+ return;
+ cpumask_clear(cm);
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
+ if ((mask & 0x1) && cpu != outgoingcpu)
+ cpumask_set_cpu(cpu, cm);
+ if (cpumask_weight(cm) == 0) {
+ cpumask_setall(cm);
+ for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
+ cpumask_clear_cpu(cpu, cm);
+ WARN_ON_ONCE(cpumask_weight(cm) == 0);
+ }
+ set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
+ rcu_boost_kthread_setaffinity(rnp, cm);
+ free_cpumask_var(cm);
+}
+
+/*
+ * Spawn a per-rcu_node kthread, setting priority and affinity.
+ * Called during boot before online/offline can happen, or, if
+ * during runtime, with the main CPU-hotplug locks held. So only
+ * one of these can be executing at a time.
+ */
+static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
+ struct rcu_node *rnp)
+{
+ unsigned long flags;
+ int rnp_index = rnp - &rsp->node[0];
+ struct sched_param sp;
+ struct task_struct *t;
+
+ if (!rcu_kthreads_spawnable ||
+ rnp->qsmaskinit == 0)
+ return 0;
+ if (rnp->node_kthread_task == NULL) {
+ t = kthread_create(rcu_node_kthread, (void *)rnp,
+ "rcun%d", rnp_index);
+ if (IS_ERR(t))
+ return PTR_ERR(t);
+ raw_spin_lock_irqsave(&rnp->lock, flags);
+ rnp->node_kthread_task = t;
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ sp.sched_priority = 99;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+ }
+ return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
+}
+
+/*
+ * Spawn all kthreads -- called as soon as the scheduler is running.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+ int cpu;
+ struct rcu_node *rnp;
+
+ rcu_kthreads_spawnable = 1;
+ for_each_possible_cpu(cpu) {
+ per_cpu(rcu_cpu_has_work, cpu) = 0;
+ if (cpu_online(cpu))
+ (void)rcu_spawn_one_cpu_kthread(cpu);
+ }
+ rnp = rcu_get_root(rcu_state);
+ (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+ if (NUM_RCU_NODES > 1) {
+ rcu_for_each_leaf_node(rcu_state, rnp)
+ (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+ }
+ return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
+static void __cpuinit rcu_prepare_kthreads(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
+ struct rcu_node *rnp = rdp->mynode;
+
+ /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+ if (rcu_kthreads_spawnable) {
+ (void)rcu_spawn_one_cpu_kthread(cpu);
+ if (rnp->node_kthread_task == NULL)
+ (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+ }
+}
+
#else /* #ifdef CONFIG_RCU_BOOST */
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1346,6 +1710,26 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}
+#ifdef CONFIG_HOTPLUG_CPU
+
+static void rcu_stop_cpu_kthread(int cpu)
+{
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
+{
+}
+
+static void __cpuinit rcu_prepare_kthreads(int cpu)
+{
+}
+
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifndef CONFIG_SMP
--
1.7.3.2
* Paul E. McKenney ([email protected]) wrote:
> This patchset banishes RCU kthreads from non-RCU_BOOST kernel threads.
> The two patches are as follows:
>
> 1. Minimal patch that #ifdefs out the kthread code.
>
> 2. Code-movement patch that puts the code #ifdefed out above
> under existing #ifdefs in kernel/rcutree_plugin.h.
Hi Paul,
I'm wondering about the impact of this change: so I guess that before
the change, it was OK to go on a waitqueue (might_sleep()) within a
call_rcu callback, but since the execution now moves to a softirq
handler in non-RCU_BOOST kernels, it's not allowed anymore. I might be
missing something though: was sleeping within call_rcu handlers already
prohibited ? (never had to sleep in those, so I never had to check if it
was allowed)
Thanks,
Mathieu
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
On Fri, Jun 17, 2011 at 04:35:23PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney ([email protected]) wrote:
> > This patchset banishes RCU kthreads from non-RCU_BOOST kernel threads.
> > The two patches are as follows:
> >
> > 1. Minimal patch that #ifdefs out the kthread code.
> >
> > 2. Code-movement patch that puts the code #ifdefed out above
> > under existing #ifdefs in kernel/rcutree_plugin.h.
>
> Hi Paul,
>
> I'm wondering about the impact of this change: so I guess that before
> the change, it was OK to go on a waitqueue (might_sleep()) within a
> call_rcu callback, but since the execution now moves to a softirq
> handler in non-RCU_BOOST kernels, it's not allowed anymore. I might be
> missing something though: was sleeping within call_rcu handlers already
> prohibited ? (never had to sleep in those, so I never had to check if it
> was allowed)
The callbacks are still executed in BH context, so any attempt to
sleep should get a warning message. Also, it switched to kthread quite
recently, so there hasn't been time for anyone to get used to it. ;-)
Thanx, Paul