linux-kernel - Re: [LKP] [lkp] [sched/fair] 53d3bc773e: hackbench.throughput -32.9% regression

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Date:	Wed, 01 Jun 2016 16:53:28 +0800
From:	"Huang\, Ying" <ying.huang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Huang\, Ying" <ying.huang@...el.com>,
	Ingo Molnar <mingo@...nel.org>, <lkp@...org>,
	Mike Galbraith <efault@....de>, <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [LKP] [lkp] [sched/fair] 53d3bc773e: hackbench.throughput -32.9% regression

Peter Zijlstra <peterz@...radead.org> writes:

> On Wed, Jun 01, 2016 at 01:00:10PM +0800, Huang, Ying wrote:
>> Hi, Peter,
>> 
>> Peter Zijlstra <peterz@...radead.org> writes:
>> 
>> > On Tue, May 31, 2016 at 04:34:36PM +0800, Huang, Ying wrote:
>> >> Hi, Ingo,
>> >> 
>> >> Part of the regression has been recovered in v4.7-rc1 from -32.9% to
>> >> -9.8%.  But there is still some regression.  Is it possible for fully
>> >> restore it?
>> >
>> > after much searching on how you guys run hackbench... I figured
>> > something like:
>> >
>> >   perf bench sched messaging -g 20 --thread -l 60000
>> 
>> There is a reproduce file attached in the original report email, its
>> contents is something like below:
>> 
>> 2016-05-15 08:57:02 echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
>
> <snip stupid large output>
>
>> 2016-05-15 09:06:24 /usr/bin/hackbench -g 24 --threads -l 60000
>> 
>> Hope that will help you for reproduce.
>
> It did not, because I didn't have the exact same machine and its not
> apparent how I should modify -- if at all -- the arguments to be
> representative when ran on my machine.
>
>> > on my IVB-EP (2*10*2) is similar to your IVT thing.
>> >
>> > And running something like:
>> >
>> >   for i in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ; do echo performance > $i ; done
>> >   perf stat --null --repeat 10 -- perf bench sched messaging -g 20 --thread -l 60000 | grep "seconds time elapsed"
>> >
>> > gets me:
>> >
>> > v4.6:
>> >
>> >       36.786914089 seconds time elapsed ( +-  0.49% )
>> >       37.054017355 seconds time elapsed ( +-  1.05% )
>> >
>> >
>> > origin/master (v4.7-rc1-ish):
>> >
>> >       34.757435264 seconds time elapsed ( +-  3.34% )
>> >       35.396252515 seconds time elapsed ( +-  3.38% )
>> >
>> >
>> > Which doesn't show a regression between v4.6 and HEAD; in fact it shows
>> > an improvement.
>> 
>> Yes.  For hackbench test, linus/master (v4.7-rc1+) is better than v4.6,
>> but it is worse than v4.6-rc7.  Details is as below.
>
> That kernel was broken.. what your point?

You mean the commit is a functionality fix?  I found the
hackbench.throughput for the test is

v4.5: 1.4e+5
v4.6-rc1~v4.6-rc7: 1.9e+5
v4.6: 1.3e+5
v4.7-rc1: 1.7e+5

So some commit in v4.6-rc1 introduce some issue but improve the score
for the test, which is fixed in v4.6, and some improvement merged by
v4.7-rc1?

Best Regards,
Huang, Ying