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>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2a99f1c..16a982e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -501,8 +501,11 @@
/*
* 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 7c9098d..01f55ad 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6541,6 +6541,11 @@
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 @@
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 @@
*/
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 @@
{
BUG_ON(!in_softirq());
- if (need_resched() && system_state == SYSTEM_RUNNING) {
+ if (should_resched()) {
local_bh_enable();
__cond_resched();
local_bh_disable();