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

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Date:	Mon, 10 Feb 2014 14:59:46 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Jason Low <jason.low2@...com>,
	Waiman Long <waiman.long@...com>, mingo@...nel.org,
	paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org,
	tglx@...utronix.de, riel@...hat.com, davidlohr@...com,
	hpa@...or.com, andi@...stfloor.org, aswin@...com,
	scott.norton@...com, chegu_vinod@...com
Subject: Re: [PATCH 6/8] mutex: Extra reschedule point

On Mon, 10 Feb 2014 20:58:26 +0100 Peter Zijlstra <peterz@...radead.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().
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