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

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Date:   Thu, 20 Oct 2016 16:32:19 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     sedat.dilek@...il.com
Cc:     Jörg Otte <jrg.otte@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Michal Marek <mmarek@...e.com>,
        Ming Lei <tom.leiming@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [4.9-rc1] Build-time 2x slower

On Thursday, October 20, 2016 04:20:44 PM Sedat Dilek wrote:
> On Thu, Oct 20, 2016 at 1:15 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Thursday, October 20, 2016 09:41:34 AM Sedat Dilek wrote:
> >> On Wed, Oct 19, 2016 at 10:55 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> > On Wednesday, October 19, 2016 06:59:35 PM Jörg Otte wrote:
> >> >> 2016-10-19 17:29 GMT+02:00 Linus Torvalds <torvalds@...ux-foundation.org>:
> >> >> > On Wed, Oct 19, 2016 at 4:07 AM, Jörg Otte <jrg.otte@...il.com> wrote:
> >> >> >>
> >> >> >> Additional info: I usally use schedutil governor.
> >> >> >> If I switch to performance governor problems go away.
> >> >> >> Maybe a cpufreq problem?
> >> >> >
> >> >> > Oh, I completely misread the original bug report, and then didn't read
> >> >> > your confirmation email right.
> >> >> >
> >> >> > I thought you had a slower build of the different kernels (when
> >> >> > building on the same kernel), and that the _build_ itself had slowed
> >> >> > down for some reason. But you're actually saying that doing the _same_
> >> >> > build actually takes longer when running on 4.9-rc1.
> >> >>
> >> >> Exactly!
> >> >>
> >> >> Btw: ondemand governor is also good.
> >> >>
> >> >> > There are a few small cpufreq changes there in between commit
> >> >> > 29fbff8698fc (that you reported was fine - please tell me I got _that_
> >> >> > right, at least?) and 4.9-rc1.
> >> >>
> >> >> Perfect! That's what I mean.
> >> >>
> >> >> > Adding Rafael to the cc.
> >> >> >
> >> >> > That said, none of them look all that likely to me. It *would* be good
> >> >> > if you could bisect it a bit (perhaps not fully, but a couple of
> >> >> > bisection steps to narrow down what area it is).
> >> >>
> >> >> I try that tomorrow.
> >> >
> >> > Well, please try commit ef98988ba369 (Merge tag 'pm-extra-4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm) which is the
> >> > merge introducing the late cpufreq changes.  If the issue is there, please
> >> > try to revert commit 899bb6642f2a (cpufreq: skip invalid entries when searching
> >> > the frequency) which is the only cpufreq one that may matter for the schedutil
> >> > governor (and I have one fix for that commit queued up already).
> >> >
> >>
> >> Is "cpufreq: fix overflow in cpufreq_table_find_index_dl()" the fix
> >> you are speaking of?
> >>
> >> Fixes: 899bb6642f2a (cpufreq: skip invalid entries when searching the frequency)
> >
> > Yes.
> >
> >> If yes, can you add a hint in the commit message describing the impact
> >> like here a slow-down of building a linux-kernel.
> >> With a reference to this ML-thread?
> >
> > I will if that turns out to be the case.
> >
> 
> I have tried the revert and the patch from Sergey Senozhatsk pending
> in linux-pm.git#linux-next.
> Both fixes the issue for me.

OK, thanks for the confirmation!

> Feel free to give appropriate credits and many thanks to Jörg.
> 
> I tried 'make -j3' in my last build and it was approx. 5mins faster in
> my customized setup.
> Will switch back to 2 parallel-make-jobs - it's safer for me.
> 
> Can you explain why this issue was not seen when building under Linux v4.8.x?
> [1] says...
> Cc: 4.8+ <stable@...r.kernel.org> # 4.8+

The commit in question might not make it into 4.8.y yet.

Thanks,
Rafael