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

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Message-ID: <51BF9960.904@intel.com>
Date:	Tue, 18 Jun 2013 07:18:56 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Tim Chen <tim.c.chen@...ux.intel.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>, Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Performance regression from switching lock to rw-sem for anon-vma
 tree

On 06/18/2013 02:45 AM, Tim Chen wrote:
>>> +			if (unlikely(sem->count < RWSEM_WAITING_BIAS)) {
>>> > > +				cpu_relax();
>>> > > +				continue;
>>> > > +			}
> The above two if statements could be cleaned up as a single check:
> 		
> 			if (unlikely(sem->count < RWSEM_WAITING_BIAS))
> 				return sem;
> 	 
> This one statement is sufficient to check that we don't have a writer
> stolen the lock before we attempt to acquire the read lock by modifying
> sem->count.  
> 
> 

Thanks. I will send out the patchset base your suggestion.


-- 
Thanks
    Alex
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