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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2009-07-10 14:57:57 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2009-07-10 14:24:05 -0700
commitd86ee4809d0329d4aa0d0f2c76c2295a16862799 (patch)
tree32b3eaf766c1127ef2298c2e48b5441b7cf9b843
parentc99e6efe1ba04561e7d93a81f0be07e37427e835 (diff)
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>
-rw-r--r--include/linux/sched.h5
-rw-r--r--kernel/sched.c14
2 files changed, 13 insertions, 6 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2a99f1c15cf..16a982e389f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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
diff --git a/kernel/sched.c b/kernel/sched.c
index 7c9098d186e..01f55ada359 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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();