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

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Date:	Tue, 31 May 2016 14:41:51 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	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

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

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.