Re: [PATCH 6/8] mutex: Extra reschedule point

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 10 Feb 2014 20:58:26 +0100 Peter Zijlstra <peterz@infradead.org> wrote:

> Add in an extra reschedule in an attempt to avoid getting reschedule
> the moment we've acquired the lock.
> 
> ...
>
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -468,6 +468,13 @@ __mutex_lock_common(struct mutex *lock,
>  	}
>  	osq_unlock(&lock->osq);
>  slowpath:
> +	/*
> +	 * If we fell out of the spin path because of need_resched(),
> +	 * reschedule now, before we try-lock the mutex. This avoids getting
> +	 * scheduled out right after we obtained the mutex.
> +	 */
> +	if (unlikely(need_resched()))
> +		schedule_preempt_disabled();

need_resched() already does unlikely().