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From: Jason Low <jason.low2@hp.com>
To: Davidlohr Bueso <dave@stgolabs.net>
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, jason.low2@hp.com
Subject: Re: [PATCH 4/6] locking/rwsem: Avoid deceiving lock spinners
Date: Thu, 29 Jan 2015 12:13:21 -0800	[thread overview]
Message-ID: <1422562401.2418.13.camel@j-VirtualBox> (raw)
In-Reply-To: <1422493812.4604.29.camel@stgolabs.net>

On Wed, 2015-01-28 at 17:10 -0800, Davidlohr Bueso wrote:

> 	if (READ_ONCE(sem->owner))
> 		return true; /* new owner, continue spinning */

In terms of the sem->owner check, I agree. This also reminds me of a
similar patch I was going to send out, but for mutex. The idea is that
before we added all the MCS logic, we wanted to return false if owner
isn't NULL to prevent too many threads simultaneously spinning on the
owner at the same time.

With the new MCS queuing, we don't have to worry about that issue, so it
makes sense to continue spinning as long as owner is running and the
spinner doesn't need to reschedule.



  reply	other threads:[~2015-01-29 20:13 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 [this message]
2015-01-29 20:18             ` Jason Low
2015-01-29 23:15               ` Davidlohr Bueso
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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