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sched: optimize cond_resched() 

Optimize cond_resched() by removing one conditional.

Currently cond_resched() checks system_state ==
SYSTEM_RUNNING in order to avoid scheduling before the
scheduler is running.

We can however, as per suggestion of Matt, use
PREEMPT_ACTIVE to accomplish that very same.

Suggested-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Zijlstra 2009-07-10 14:57:57 +02:00 committed by Linus Torvalds
parent c99e6efe1b
commit d86ee4809d
2 changed files with 13 additions and 6 deletions
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5
include/linux/sched.h
View File

@ -501,8 +501,11 @@ struct task_cputime {
/*
* Disable preemption until the scheduler is running.
* Reset by start_kernel()->sched_init()->init_idle().
*
* We include PREEMPT_ACTIVE to avoid cond_resched() from working
* before the scheduler is active -- see should_resched().
*/
#define INIT_PREEMPT_COUNT (1)
#define INIT_PREEMPT_COUNT (1 + PREEMPT_ACTIVE)
/**
* struct thread_group_cputimer - thread group interval timer counts

14
kernel/sched.c
View File

@ -6541,6 +6541,11 @@ SYSCALL_DEFINE0(sched_yield)
return 0;
}
static inline int should_resched(void)
{
return need_resched() && !(preempt_count() & PREEMPT_ACTIVE);
}
static void __cond_resched(void)
{
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
@ -6560,8 +6565,7 @@ static void __cond_resched(void)
int __sched _cond_resched(void)
{
if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
system_state == SYSTEM_RUNNING) {
if (should_resched()) {
__cond_resched();
return 1;
}
@ -6579,12 +6583,12 @@ EXPORT_SYMBOL(_cond_resched);
*/
int cond_resched_lock(spinlock_t *lock)
{
int resched = need_resched() && system_state == SYSTEM_RUNNING;
int resched = should_resched();
int ret = 0;
if (spin_needbreak(lock) || resched) {
spin_unlock(lock);
if (resched && need_resched())
if (resched)
__cond_resched();
else
cpu_relax();
@ -6599,7 +6603,7 @@ int __sched cond_resched_softirq(void)
{
BUG_ON(!in_softirq());
if (need_resched() && system_state == SYSTEM_RUNNING) {
if (should_resched()) {
local_bh_enable();
__cond_resched();
local_bh_disable();