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Commit d86ee480 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Linus Torvalds
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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: default avatarMatt Mackall <mpm@selenic.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarMatt Mackall <mpm@selenic.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c99e6efe

include/linux/sched.h

+4 −1
Original line number Diff line number Diff line
@@ -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

kernel/sched.c

+9 −5
Original line number Diff line number Diff line
@@ -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();