linux-kernel - Re: [PATCH v5 0/6] rwsem: performance optimizations

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Message-ID: <1380079935.2163.3.camel@buesod1.americas.hpqcorp.net>
Date:	Tue, 24 Sep 2013 20:32:15 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v5 0/6]  rwsem: performance optimizations

On Tue, 2013-09-24 at 15:22 -0700, Tim Chen wrote:
> We have incorporated various suggestions from Ingo for version 5 of this patchset
> and will like to have it merged if there are no objections.
> 
> In this patchset, we introduce two categories of optimizations to read
> write semaphore.  The first four patches from Alex Shi reduce cache bouncing of the
> sem->count field by doing a pre-read of the sem->count and avoid cmpxchg
> if possible.
> 
> The last two patches introduce similar optimistic spinning logic as
> the mutex code for the writer lock acquisition of rwsem.

Right. We address the general 'mutexes out perform writer-rwsems'
situations that has been seen in more than one case. Users now need not
worry about performance issues when choosing between these two locking
mechanisms.

Thanks,
Davidlohr


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