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Subject[tip:sched/core] sched: Drop the need_resched() loop from cond_resched()
Commit-ID:  e7aaaa6934636d7a6cadd9e2a05250fbb6a34f65
Gitweb: http://git.kernel.org/tip/e7aaaa6934636d7a6cadd9e2a05250fbb6a34f65
Author: Frederic Weisbecker <fweisbec@gmail.com>
AuthorDate: Thu, 16 Jul 2009 15:44:29 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 18 Jul 2009 15:51:38 +0200
sched: Drop the need_resched() loop from cond_resched()

The schedule() function is a loop that reschedules the current
task while the TIF_NEED_RESCHED flag is set:

void schedule(void)
{
need_resched:
/* schedule code */
if (need_resched())
goto need_resched;
}
And cond_resched() repeat this loop:

do {
add_preempt_count(PREEMPT_ACTIVE);
schedule();
sub_preempt_count(PREEMPT_ACTIVE);
} while(need_resched());
This loop is needless because schedule() already did the check
and nothing can set TIF_NEED_RESCHED between schedule() exit
and the loop check in need_resched().

Then remove this needless loop.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1247725694-6082-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/sched.c | 8 +++-----
1 files changed, 3 insertions(+), 5 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 03f7e3f..4c5ee84 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6618,11 +6618,9 @@ static void __cond_resched(void)
* PREEMPT_ACTIVE, which could trigger a second
* cond_resched() call.
*/
- do {
- add_preempt_count(PREEMPT_ACTIVE);
- schedule();
- sub_preempt_count(PREEMPT_ACTIVE);
- } while (need_resched());
+ add_preempt_count(PREEMPT_ACTIVE);
+ schedule();
+ sub_preempt_count(PREEMPT_ACTIVE);
}

int __sched _cond_resched(void)

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