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

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Message-ID: <2813073.ZhfuKSkB6i@vostro.rjw.lan>
Date:   Thu, 20 Oct 2016 13:15:58 +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>
Subject: Re: [4.9-rc1] Build-time 2x slower

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.

Thanks,
Rafael