linux-kernel - Re: [lkp] [x86/platform/UV] 71854cb812: will-it-scale.per_thread

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Date:   Fri, 28 Oct 2016 00:37:45 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ye Xiaolong <xiaolong.ye@...el.com>
cc:     Alex Thorlton <athorlton@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Travis <travis@....com>, Russ Anderson <rja@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        x86@...nel.org, lkp@...org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [lkp] [x86/platform/UV] 71854cb812: will-it-scale.per_thread_ops
 -2.3% regression

On Thu, 27 Oct 2016, Ye Xiaolong wrote:
> Yes, this is weird, the per_thread_ops change is small and should be run
> to run variation, the actual significant change is will-it-scale.time.user_time
> -27% decrease, but the patch seems not relevant, we can't interpret it. :(
> 
> We've tried to queue the jobs (4 times) for
> 71854cb812ec23bfe5f63d52217e6b9e6cb901f5 and v4.9-rc1 with new kconfig
> (added CONFIG_DEBUG_INFO_REDUCED), and result shows user_time change is
> quite stable.

>         v4.9-rc1 71854cb812ec23bfe5f63d5221
> ---------------- -------------------------- 
>          %stddev     %change         %stddev
>              \          |                \
>    1670068 ±  0%      -3.8%    1606650 ±  1%  will-it-scale.per_thread_ops
>       9749 ±  2%   +1328.0%     139222 ±105%  will-it-scale.time.involuntary_context_switches

	     	     		  ^^^^^^ This is massive

I have no explanation for this either, but you really should try to figure
out what's going on here.

The only difference between plain rc1 and rc + this patch is the resulting
text size and therefor some other unrelated stuff moving to different
places in memory which has some yet to figure out side effects.

Thanks,

	tglx