Re: [PATCH 1/2] sched: Drop the need_resched() loop from cond_resched()

Peter Zijlstra
2009-07-10T15:00:58Z

On Fri, 2009-07-10 at 16:49 +0200, Frederic Weisbecker wrote:
> 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>

> ---
> kernel/sched.c | 8 +++-----
> 1 files changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 4d1e387..87ecac1 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -6613,11 +6613,9 @@ 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)