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Date: Thu, 14 Apr 2011 08:39:51 GMT
From: tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
tglx@...utronix.de, frank.rowand@...sony.com, mingo@...e.hu
Subject: [tip:sched/locking] sched: Move the second half of ttwu() to the remote cpu
Commit-ID: 317f394160e9beb97d19a84c39b7e5eb3d7815a8
Gitweb: http://git.kernel.org/tip/317f394160e9beb97d19a84c39b7e5eb3d7815a8
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Tue, 5 Apr 2011 17:23:58 +0200
Committer: Ingo Molnar <mingo@...e.hu>
CommitDate: Thu, 14 Apr 2011 08:52:41 +0200
sched: Move the second half of ttwu() to the remote cpu
Now that we've removed the rq->lock requirement from the first part of
ttwu() and can compute placement without holding any rq->lock, ensure
we execute the second half of ttwu() on the actual cpu we want the
task to run on.
This avoids having to take rq->lock and doing the task enqueue
remotely, saving lots on cacheline transfers.
As measured using: http://oss.oracle.com/~mason/sembench.c
$ for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance > $i; done
$ echo 4096 32000 64 128 > /proc/sys/kernel/sem
$ ./sembench -t 2048 -w 1900 -o 0
unpatched: run time 30 seconds 647278 worker burns per second
patched: run time 30 seconds 816715 worker burns per second
Reviewed-by: Frank Rowand <frank.rowand@...sony.com>
Cc: Mike Galbraith <efault@....de>
Cc: Nick Piggin <npiggin@...nel.dk>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/20110405152729.515897185@chello.nl
---
include/linux/sched.h | 3 +-
init/Kconfig | 5 ++++
kernel/sched.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++
kernel/sched_features.h | 6 +++++
4 files changed, 69 insertions(+), 1 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 25c5031..e09dafa 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1203,6 +1203,7 @@ struct task_struct {
int lock_depth; /* BKL lock depth */
#ifdef CONFIG_SMP
+ struct task_struct *wake_entry;
int on_cpu;
#endif
int on_rq;
@@ -2192,7 +2193,7 @@ extern void set_task_comm(struct task_struct *tsk, char *from);
extern char *get_task_comm(char *to, struct task_struct *tsk);
#ifdef CONFIG_SMP
-static inline void scheduler_ipi(void) { }
+void scheduler_ipi(void);
extern unsigned long wait_task_inactive(struct task_struct *, long match_state);
#else
static inline void scheduler_ipi(void) { }
diff --git a/init/Kconfig b/init/Kconfig
index 56240e7..32745bf 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -827,6 +827,11 @@ config SCHED_AUTOGROUP
desktop applications. Task group autogeneration is currently based
upon task session.
+config SCHED_TTWU_QUEUE
+ bool
+ depends on !SPARC32
+ default y
+
config MM_OWNER
bool
diff --git a/kernel/sched.c b/kernel/sched.c
index 7d8b85f..9e3ede1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -556,6 +556,10 @@ struct rq {
unsigned int ttwu_count;
unsigned int ttwu_local;
#endif
+
+#ifdef CONFIG_SMP
+ struct task_struct *wake_list;
+#endif
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
@@ -2516,10 +2520,61 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
return ret;
}
+#ifdef CONFIG_SMP
+static void sched_ttwu_pending(void)
+{
+ struct rq *rq = this_rq();
+ struct task_struct *list = xchg(&rq->wake_list, NULL);
+
+ if (!list)
+ return;
+
+ raw_spin_lock(&rq->lock);
+
+ while (list) {
+ struct task_struct *p = list;
+ list = list->wake_entry;
+ ttwu_do_activate(rq, p, 0);
+ }
+
+ raw_spin_unlock(&rq->lock);
+}
+
+void scheduler_ipi(void)
+{
+ sched_ttwu_pending();
+}
+
+static void ttwu_queue_remote(struct task_struct *p, int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+ struct task_struct *next = rq->wake_list;
+
+ for (;;) {
+ struct task_struct *old = next;
+
+ p->wake_entry = next;
+ next = cmpxchg(&rq->wake_list, old, p);
+ if (next == old)
+ break;
+ }
+
+ if (!next)
+ smp_send_reschedule(cpu);
+}
+#endif
+
static void ttwu_queue(struct task_struct *p, int cpu)
{
struct rq *rq = cpu_rq(cpu);
+#if defined(CONFIG_SMP) && defined(CONFIG_SCHED_TTWU_QUEUE)
+ if (sched_feat(TTWU_QUEUE) && cpu != smp_processor_id()) {
+ ttwu_queue_remote(p, cpu);
+ return;
+ }
+#endif
+
raw_spin_lock(&rq->lock);
ttwu_do_activate(rq, p, 0);
raw_spin_unlock(&rq->lock);
@@ -6331,6 +6386,7 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
#ifdef CONFIG_HOTPLUG_CPU
case CPU_DYING:
+ sched_ttwu_pending();
/* Update our root-domain */
raw_spin_lock_irqsave(&rq->lock, flags);
if (rq->rd) {
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index 68e69ac..be40f73 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -64,3 +64,9 @@ SCHED_FEAT(OWNER_SPIN, 1)
* Decrement CPU power based on irq activity
*/
SCHED_FEAT(NONIRQ_POWER, 1)
+
+/*
+ * Queue remote wakeups on the target CPU and process them
+ * using the scheduler IPI. Reduces rq->lock contention/bounces.
+ */
+SCHED_FEAT(TTWU_QUEUE, 1)
--
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