Re: Performance regression in v3.14

[Dirk Brandewie]

On 05/06/2014 10:40 PM, Viresh Kumar wrote:
> Cc'ing Dirk who is taking care of intel-pstate driver.

Thanks Viresh I had seen this thread.

I am looking into it

--Dirk
> On 6 May 2014 22:05, Johan Hovold <jhovold@xxxxxxxxx> wrote:
> > After updating my main system from v3.13 to v3.14.2, I found that the
> > git bash-completion was extremely sluggish. Completing a file name would
> > take roughly six rather than one second on this Haswell machine
> > (i7-4770). (Other things, such as git rebase, also felt slower, but
> > the completion issue was much more obvious and easy to measure).
> >
> > I managed to reproduce the problem using the following minimal construct
> >
> >          cat dmesg.repeat | while read x; do true; done
> >
> > where dmesg.repeat is simply dmesg concatenated together to an
> > equivalent number of lines as produced by git ls-files in the
> > kernel-source tree root (45k), and where the actual processing of each
> > line has been removed.
> >
> > Most of the time I get:
> >
> >          $ time cat dmesg.repeat | while read x; do true; done
> >
> >          real    0m6.091s
> >          user    0m3.674s
> >          sys     0m2.447s
> >
> > but sometimes it only takes one second.
> >
> >          $ time cat dmesg.repeat | while read x; do true; done
> >
> >          real    0m1.100s
> >          user    0m0.544s
> >          sys     0m0.570s
> >
> > I don't seem to be able to reproduce the problem on 3.13 where the pipe
> > always takes about one second to finish.
> >
> > Taking all but one core offline seems to make the problem go away, and so
> > does using the performance rather than powersave governor of the
> > intel_pstate cpufreq driver (on at least one of two online cores).
> >
> > Moving the mouse cursor makes to loop finish faster, and so does
> > switching to a another terminal to print cpufreq/cpuinfo_cur_freq which
> > was around cpuinfo_min_freq several times (when tracing, see below).
> >
> > I could not reproduce the problem when using perf record, but I can get
> > function-profile traces using ftrace (in which case the loop takes about
> > 60 seconds instead of six seconds to finish).
> >
> > Comparing the traces I see a lot of functions taking ten times longer to
> > finish, but I guess that's expected if this is indeed a cpufreq issue.
> >
> > Since this is my main machine (and only multi-core machine at the
> > moment) I'm not able to bisect this myself. And for the same reason I
> > have not verified that the problem persists in v3.15-rc.
> >
> > I don't see any cpufreq patches in the v3.14.3 stable queue nor anything
> > obviously related and marked for stable in v3.15-rc.
> >
> > Any ideas about what might be going on?
>
> I tried to take a look at the diff for cpufreq between 3.13 and 3.14.2 and
> couldn't pin point on any change which might cause it. Don't have a clue
> of what's going on. I don't know how to help you on this.
>
> Normally I test my stuff on a ARM board and I don't remember facing
> any such behavior there. There might be something wrong with intel-pstate
> as well..
>
> Also, can you try to use acpi-cpufreq instead? And see how that is behaving?
>
> --
> viresh

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