linux-kernel - Re: Performance regression from switching lock to rw-sem for anon-vma tree

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Date:	Mon, 17 Jun 2013 15:27:46 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>,
	Ingo Molnar <mingo@...e.hu>, Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>, "Shi, Alex" <alex.shi@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: Performance regression from switching lock to rw-sem for
 anon-vma tree

On Fri, 2013-06-14 at 15:47 -0700, Michel Lespinasse wrote:
> On Fri, Jun 14, 2013 at 3:31 PM, Davidlohr Bueso <davidlohr.bueso@...com> wrote:
> > A few ideas that come to mind are avoiding taking the ->wait_lock and
> > avoid dealing with waiters when doing the optimistic spinning (just like
> > mutexes do).
> >
> > I agree that we should first deal with the optimistic spinning before
> > adding the MCS complexity.
> 
> Maybe it would be worth disabling the MCS patch in mutex and comparing
> that to the rwsem patches ? Just to make sure the rwsem performance
> delta isn't related to that.
> 

I've tried to back out the MCS patch.  In fact, for exim, it is about 1%
faster without MCS.  So the better performance of mutex I saw was not
due to MCS.  Thanks for the suggestion.

Tim

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