linux-kernel - Re: [LKP] [futex] 76835b0ebf8: -8.1% will-it-scale.per_thread

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Date:	Fri, 27 Feb 2015 11:28:51 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, LKP ML <lkp@...org>
Subject: Re: [LKP] [futex] 76835b0ebf8: -8.1% will-it-scale.per_thread_ops

Hi, Catalin,

On Thu, 2015-02-26 at 09:58 +0000, Catalin Marinas wrote:
> On Thu, Feb 26, 2015 at 05:16:53AM +0000, Huang Ying wrote:
> > FYI, we noticed the below changes on
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > commit 76835b0ebf8a7fe85beb03c75121419a7dec52f0 ("futex: Ensure get_futex_key_refs() always implies a barrier")
> > 
> > 
> > testbox/testcase/testparams: lkp-wsx01/will-it-scale/performance-futex4
> > 
> > 0429fbc0bdc297d6  76835b0ebf8a7fe85beb03c751
> > ----------------  --------------------------
> >          %stddev     %change         %stddev
> >              \          |                \
> >    6314259 ±  0%      -8.1%    5800079 ±  0%  will-it-scale.per_thread_ops
> >    6274871 ±  0%      -8.1%    5768747 ±  0%  will-it-scale.per_process_ops
> 
> This was raised before but I'm not sure we can do much about it:
> 
> https://lkml.org/lkml/2014/10/26/189

Sorry for duplicated report.

> It would be interesting to know the difference in performance with the
> code prior to commits b0c29f79ecea and 11d4616bd07f which optimised the
> futex code but missed a barrier.

I will do some test for that.

Best Regards,
Huang, Ying


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