Re: [4.9-rc1] Build-time 2x slower

From	Jörg Otte <jrg.otte@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [4.9-rc1] Build-time 2x slower
Date	2016-10-19 17:30 +0200
Message-ID	<su0Yx-33U-29@gated-at.bofh.it> (permalink)
References	<stiEa-5Hd-13@gated-at.bofh.it> <strxL-3nR-7@gated-at.bofh.it> <stz2h-8dA-3@gated-at.bofh.it> <stFU5-4q4-9@gated-at.bofh.it> <stGdr-4O9-29@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

2016-10-18 19:19 GMT+02:00 Linus Torvalds <torvalds@linux-foundation.org>:
> On Tue, Oct 18, 2016 at 9:49 AM, Jörg Otte <jrg.otte@gmail.com> wrote:
>> On Tue, Oct 18, 2016 at 12:04 AM, Sedat Dilek <sedat.dilek@gmail.com> wrote:
>>>
>>> not sure whom to address on this issue.
>>>
>>> I have built Linux v4.9-rc1, v4.8.2 and v4.4.25 kernels (in this
>>> order) this morning.
>>>
>>> Building a Linux v4.8.2 under Linux v4.9-rc1 took two times longer.
>>>
>>> As usually I build with 2 parallel-make-jobs.
>>> This takes approx. 30mins.
>>> Under Linux v4.9-rc1 it took approx. an hour.
>>>
>>> My system is a Ubuntu/precise AMD64 (WUBI installation).
>>> I use my normal build-environment.
>>
>> I can confirm the problem. I use 3 build jobs in parallel
>> and the kernel build takes 2,5 times longer.
>>
>> I'm only seeing 1 (of 4) cores are running with max frequency.
>> The other are running in minimum frequency. And this seems not
>> to be limited to build jobs however.
>>
>> The last known good kernel for me is  ..-4.8.0-14604-g29fbff8
>
> Well, there are a few merges in 4.9-rc1 since that
> 4.8.0-14604-g29fbff8 version, but the obvious ones are my pulls from:
>
>   Michal Marek (2):
>      kbuild updates
>      misc kbuild changes
>
> (My merge commit ID's are 50cff89837a4 and 84d69848c97f) with
> everything else looking like "normal code updates".
>
> Michal: a 2.5x slowdown of the kernel build was presumably *not* intentional.
>
> I'm not seeing anything obvious, but if it's spending a lot more time
> in fixdep, then it's that "strstr()" change. That commit seems to
> assume that strstr() is fast, which is a debatable assumption and
> might be wrong in some environments.
>
> But even with a "strstr()" written by a sloth that was dropped on its
> head a few too many times when young, I can't see it being *that* much
> slower.
>
> Can you do just a silly
>
>    perf record make -j8
>
> of the bad build, and see if something stands out when you do "perf report"?
>
> But maybe Michal has some ideas.
>
>               Linus

Additional info: I usally use schedutil governor.
If I switch to performance governor problems go away.
Maybe a cpufreq problem?

Jörg

Thread

Re: [4.9-rc1] Build-time 2x slower Ming Lei <tom.leiming@gmail.com> - 2016-10-18 03:40 +0200
  Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-18 11:40 +0200
    Re: [4.9-rc1] Build-time 2x slower Jörg Otte <jrg.otte@gmail.com> - 2016-10-18 19:00 +0200
      Re: [4.9-rc1] Build-time 2x slower Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-18 19:20 +0200
        Re: [4.9-rc1] Build-time 2x slower Jörg Otte <jrg.otte@gmail.com> - 2016-10-19 17:30 +0200
          Re: [4.9-rc1] Build-time 2x slower Linus Torvalds <torvalds@linux-foundation.org> - 2016-10-19 17:30 +0200
            Re: [4.9-rc1] Build-time 2x slower Jörg Otte <jrg.otte@gmail.com> - 2016-10-19 19:00 +0200
              Re: [4.9-rc1] Build-time 2x slower "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-10-19 22:50 +0200
                Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-20 09:50 +0200
                Re: [4.9-rc1] Build-time 2x slower "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-10-20 13:10 +0200
                Re: [4.9-rc1] Build-time 2x slower "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-10-20 16:30 +0200
                Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-20 16:40 +0200
                Re: [4.9-rc1] Build-time 2x slower "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-10-20 16:50 +0200
                Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-21 03:00 +0200
                Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-20 16:30 +0200
                Re: [4.9-rc1] Build-time 2x slower Jörg Otte <jrg.otte@gmail.com> - 2016-10-20 10:00 +0200
                Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-20 10:10 +0200
                Re: [4.9-rc1] Build-time 2x slower "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-10-20 13:10 +0200
                Re: [4.9-rc1] Build-time 2x slower Jörg Otte <jrg.otte@gmail.com> - 2016-10-20 16:40 +0200
                Re: [4.9-rc1] Build-time 2x slower "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-10-20 16:50 +0200
              Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-20 09:30 +0200
            Re: [4.9-rc1] Build-time 2x slower Sedat Dilek <sedat.dilek@gmail.com> - 2016-10-20 09:50 +0200

csiph-web