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From: Davidlohr Bueso <dave@stgolabs.net>
To: Jason Low <jason.low2@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Michel Lespinasse <walken@google.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/6] locking/rwsem: Avoid deceiving lock spinners
Date: Thu, 29 Jan 2015 15:15:26 -0800	[thread overview]
Message-ID: <1422573326.2005.7.camel@stgolabs.net> (raw)
In-Reply-To: <1422562731.2418.16.camel@j-VirtualBox>

On Thu, 2015-01-29 at 12:18 -0800, Jason Low wrote:
>  	/*
> -	 * We break out the loop above on need_resched() and when the
> -	 * owner changed, which is a sign for heavy contention. Return
> -	 * success only when lock->owner is NULL.
> +	 * We break out the loop above on either need_resched(), when
> +	 * the owner is not running, or when the lock owner changed.
> +	 * Return success only when the lock owner changed.
>  	 */
> -	return lock->owner == NULL;
> +	return lock->owner != owner;
>  }

Ideally we would refactor all this, along with getting rid of
owner_running() at some point. It no longer makes sense to split up
mutex_spin_on_owner() and we're doing duplicate owner checks. It would
also be simpler than having to guess why we broke out of the loop, for
example.


  reply	other threads:[~2015-01-29 23:15 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-26  7:36 [PATCH -tip 0/6] rwsem: Fine tuning Davidlohr Bueso
2015-01-26  7:36 ` [PATCH 1/6] locking/rwsem: Use task->state helpers Davidlohr Bueso
2015-02-04 14:38   ` [tip:locking/core] " tip-bot for Davidlohr Bueso
2015-01-26  7:36 ` [PATCH 2/6] locking/rwsem: Document barrier need when waking tasks Davidlohr Bueso
2015-01-27 17:07   ` Peter Zijlstra
2015-01-27 20:30     ` Davidlohr Bueso
2015-01-26  7:36 ` [PATCH 3/6] locking/rwsem: Set lock ownership ASAP Davidlohr Bueso
2015-01-27 17:10   ` Peter Zijlstra
2015-01-27 19:18     ` Davidlohr Bueso
2015-01-26  7:36 ` [PATCH 4/6] locking/rwsem: Avoid deceiving lock spinners Davidlohr Bueso
2015-01-27 17:23   ` Jason Low
2015-01-28  3:54     ` Davidlohr Bueso
2015-01-28 17:01       ` Tim Chen
2015-01-28 21:03       ` Jason Low
2015-01-29  1:10         ` Davidlohr Bueso
2015-01-29 20:13           ` Jason Low
2015-01-29 20:18             ` Jason Low
2015-01-29 23:15               ` Davidlohr Bueso [this message]
2015-01-30  1:52                 ` Refactoring mutex spin on owner code Jason Low
2015-01-30  7:14                   ` Davidlohr Bueso
2015-01-30  7:51                     ` Peter Zijlstra
2015-01-26  7:36 ` [PATCH 5/6] locking/rwsem: Optimize slowpath/sleeping Davidlohr Bueso
2015-01-27 17:34   ` Peter Zijlstra
2015-01-27 21:57     ` Davidlohr Bueso
2015-01-26  7:36 ` [PATCH 6/6] locking/rwsem: Check for active lock before bailing on spinning Davidlohr Bueso
2015-01-27 18:11   ` Jason Low

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