by Paul E. McKenney

[permalink] [raw]

Subject: [PATCH tip/core/rcu 1/4] Kconfig help needs to say that TREE_PREEMPT_RCU scales down

To quote Valdis:

This leaves somebody who has a laptop wondering which choice
is best for a system with only one or two cores that has
CONFIG_PREEMPT defined. One choice says it scales down nicely,
the other explicitly has a 'depends on PREEMPT' attached to it...

So add "scales down nicely" to TREE_PREEMPT_RCU to match that of
TREE_RCU.

Suggested-by: Valdis Kletnieks <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
---
init/Kconfig | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 8e8b76d..4c2c936 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -331,7 +331,8 @@ config TREE_PREEMPT_RCU
This option selects the RCU implementation that is
designed for very large SMP systems with hundreds or
thousands of CPUs, but for which real-time response
- is also required.
+ is also required. It also scales down nicely to
+ smaller systems.

endchoice

--
1.5.2.5

2009-09-13 16:15:41

by Paul E. McKenney

[permalink] [raw]

Subject: [PATCH tip/core/rcu 4/4] Fix synchronize_rcu() for TREE_PREEMPT_RCU

From: Paul E. McKenney <[email protected]>

The redirection of synchronize_sched() to synchronize_rcu() was appropriate
for TREE_RCU, but not for TREE_PREEMPT_RCU. Fix this by creating an
underlying synchronize_sched(). TREE_RCU then redirects synchronize_rcu()
to synchronize_sched(), while TREE_PREEMPT_RCU has its own version of
synchronize_rcu().

Signed-off-by: Paul E. McKenney <[email protected]>
---
include/linux/rcupdate.h | 23 +++++------------------
include/linux/rcutree.h | 4 ++--
kernel/rcupdate.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 50 insertions(+), 21 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 95e0615..39dce83 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -52,8 +52,13 @@ struct rcu_head {
};

/* Exported common interfaces */
+#ifdef CONFIG_TREE_PREEMPT_RCU
extern void synchronize_rcu(void);
+#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+#define synchronize_rcu synchronize_sched
+#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
extern void synchronize_rcu_bh(void);
+extern void synchronize_sched(void);
extern void rcu_barrier(void);
extern void rcu_barrier_bh(void);
extern void rcu_barrier_sched(void);
@@ -262,24 +267,6 @@ struct rcu_synchronize {
extern void wakeme_after_rcu(struct rcu_head *head);

/**
- * synchronize_sched - block until all CPUs have exited any non-preemptive
- * kernel code sequences.
- *
- * This means that all preempt_disable code sequences, including NMI and
- * hardware-interrupt handlers, in progress on entry will have completed
- * before this primitive returns. However, this does not guarantee that
- * softirq handlers will have completed, since in some kernels, these
- * handlers can run in process context, and can block.
- *
- * This primitive provides the guarantees made by the (now removed)
- * synchronize_kernel() API. In contrast, synchronize_rcu() only
- * guarantees that rcu_read_lock() sections will have completed.
- * In "classic RCU", these two guarantees happen to be one and
- * the same, but can differ in realtime RCU implementations.
- */
-#define synchronize_sched() __synchronize_sched()
-
-/**
* 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
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index a893077..00d08c0 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -53,6 +53,8 @@ static inline void __rcu_read_unlock(void)
preempt_enable();
}

+#define __synchronize_sched() synchronize_rcu()
+
static inline void exit_rcu(void)
{
}
@@ -68,8 +70,6 @@ static inline void __rcu_read_unlock_bh(void)
local_bh_enable();
}

-#define __synchronize_sched() synchronize_rcu()
-
extern void call_rcu_sched(struct rcu_head *head,
void (*func)(struct rcu_head *rcu));

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index bd5d5c8..28d2f24 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -74,6 +74,8 @@ void wakeme_after_rcu(struct rcu_head *head)
complete(&rcu->completion);
}

+#ifdef CONFIG_TREE_PREEMPT_RCU
+
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
@@ -87,7 +89,7 @@ void synchronize_rcu(void)
{
struct rcu_synchronize rcu;

- if (rcu_blocking_is_gp())
+ if (!rcu_scheduler_active)
return;

init_completion(&rcu.completion);
@@ -98,6 +100,46 @@ void synchronize_rcu(void)
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

+#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+
+/**
+ * synchronize_sched - wait until an rcu-sched grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu-sched
+ * grace period has elapsed, in other words after all currently executing
+ * rcu-sched read-side critical sections have completed. These read-side
+ * critical sections are delimited by rcu_read_lock_sched() and
+ * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
+ * local_irq_disable(), and so on may be used in place of
+ * rcu_read_lock_sched().
+ *
+ * This means that all preempt_disable code sequences, including NMI and
+ * hardware-interrupt handlers, in progress on entry will have completed
+ * before this primitive returns. However, this does not guarantee that
+ * softirq handlers will have completed, since in some kernels, these
+ * handlers can run in process context, and can block.
+ *
+ * This primitive provides the guarantees made by the (now removed)
+ * synchronize_kernel() API. In contrast, synchronize_rcu() only
+ * guarantees that rcu_read_lock() sections will have completed.
+ * In "classic RCU", these two guarantees happen to be one and
+ * the same, but can differ in realtime RCU implementations.
+ */
+void synchronize_sched(void)
+{
+ struct rcu_synchronize rcu;
+
+ if (rcu_blocking_is_gp())
+ return;
+
+ init_completion(&rcu.completion);
+ /* Will wake me after RCU finished. */
+ call_rcu_sched(&rcu.head, wakeme_after_rcu);
+ /* Wait for it. */
+ wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(synchronize_sched);
+
/**
* synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
*
--
1.5.2.5