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

Peter Zijlstra
2016-06-01T08:40:46Z

On Wed, Jun 01, 2016 at 01:00:10PM +0800, Huang, Ying wrote:
> Hi, Peter,
>
> Peter Zijlstra <peterz@infradead.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?