linux-kernel - Re: [lkp] [mm/vmstat] 6cdb18ad98: -8.5% will-it-scale.per_thread

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Date:	Thu, 7 Jan 2016 12:23:01 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	kernel test robot <ying.huang@...ux.intel.com>
Cc:	lkp@...org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [lkp] [mm/vmstat] 6cdb18ad98: -8.5% will-it-scale.per_thread_ops

On Wed, Jan 06, 2016 at 11:20:55AM +0800, kernel test robot wrote:
> FYI, we noticed the below changes on
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> commit 6cdb18ad98a49f7e9b95d538a0614cde827404b8 ("mm/vmstat: fix overflow in mod_zone_page_state()")
> 
> 
> =========================================================================================
> compiler/cpufreq_governor/kconfig/rootfs/tbox_group/test/testcase:
>   gcc-4.9/performance/x86_64-rhel/debian-x86_64-2015-02-07.cgz/ivb42/pread1/will-it-scale
> 
> commit: 
>   cc28d6d80f6ab494b10f0e2ec949eacd610f66e3
>   6cdb18ad98a49f7e9b95d538a0614cde827404b8
> 
> cc28d6d80f6ab494 6cdb18ad98a49f7e9b95d538a0 
> ---------------- -------------------------- 
>          %stddev     %change         %stddev
>              \          |                \  
>    2733943 ±  0%      -8.5%    2502129 ±  0%  will-it-scale.per_thread_ops
>       3410 ±  0%      -2.0%       3343 ±  0%  will-it-scale.time.system_time
>     340.08 ±  0%     +19.7%     406.99 ±  0%  will-it-scale.time.user_time
>   69882822 ±  2%     -24.3%   52926191 ±  5%  cpuidle.C1-IVT.time
>     340.08 ±  0%     +19.7%     406.99 ±  0%  time.user_time
>     491.25 ±  6%     -17.7%     404.25 ±  7%  numa-vmstat.node0.nr_alloc_batch
>       2799 ± 20%     -36.6%       1776 ±  0%  numa-vmstat.node0.nr_mapped
>     630.00 ±140%    +244.4%       2169 ±  1%  numa-vmstat.node1.nr_inactive_anon

Hmm... this is odd. I did review all callers of mod_zone_page_state() and
couldn't find anything obvious that would go wrong after the int -> long
change.

I also tried the "pread1_threads" test case from
https://github.com/antonblanchard/will-it-scale.git

However the results seem to vary a lot after a reboot(!), at least on s390.

So I'm not sure if this is really a regression.

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