linux-kernel - Re: [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression

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Date:	Mon, 6 Jun 2016 12:51:36 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	kernel test robot <xiaolong.ye@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.com>,
	Minchan Kim <minchan@...nel.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...nel.org>,
	Vinayak Menon <vinmenon@...eaurora.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression

On Mon, Jun 06, 2016 at 10:27:24AM +0800, kernel test robot wrote:
> 
> FYI, we noticed a -6.3% regression of unixbench.score due to commit:
> 
> commit 5c0a85fad949212b3e059692deecdeed74ae7ec7 ("mm: make faultaround produce old ptes")
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: unixbench
> on test machine: lituya: 16 threads Haswell High-end Desktop (i7-5960X 3.0G) with 16G memory
> with following parameters: cpufreq_governor=performance/nr_task=1/test=shell8
> 
> 
> Details are as below:
> -------------------------------------------------------------------------------------------------->
> 
> 
> =========================================================================================
> compiler/cpufreq_governor/kconfig/nr_task/rootfs/tbox_group/test/testcase:
>   gcc-4.9/performance/x86_64-rhel/1/debian-x86_64-2015-02-07.cgz/lituya/shell8/unixbench
> 
> commit: 
>   4b50bcc7eda4d3cc9e3f2a0aa60e590fedf728c5
>   5c0a85fad949212b3e059692deecdeed74ae7ec7
> 
> 4b50bcc7eda4d3cc 5c0a85fad949212b3e059692de 
> ---------------- -------------------------- 
>        fail:runs  %reproduction    fail:runs
>            |             |             |    
>           3:4          -75%            :4     kmsg.DHCP/BOOTP:Reply_not_for_us,op[#]xid[#]
>          %stddev     %change         %stddev
>              \          |                \  
>      14321 ±  0%      -6.3%      13425 ±  0%  unixbench.score
>    1996897 ±  0%      -6.1%    1874635 ±  0%  unixbench.time.involuntary_context_switches
>  1.721e+08 ±  0%      -6.2%  1.613e+08 ±  0%  unixbench.time.minor_page_faults
>     758.65 ±  0%      -3.0%     735.86 ±  0%  unixbench.time.system_time
>     387.66 ±  0%      +5.4%     408.49 ±  0%  unixbench.time.user_time
>    5950278 ±  0%      -6.2%    5583456 ±  0%  unixbench.time.voluntary_context_switches

That's weird.

I don't understand why the change would reduce number or minor faults.
It should stay the same on x86-64. Rise of user_time is puzzling too.

Hm. Is reproducible? Across reboot?

-- 
 Kirill A. Shutemov