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

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Date:   Thu, 20 Oct 2016 13:14:32 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Jörg Otte <jrg.otte@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Michal Marek <mmarek@...e.com>,
        Sedat Dilek <sedat.dilek@...il.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 09:57:45 AM Jörg Otte wrote:
> 2016-10-19 22:55 GMT+02:00 Rafael J. Wysocki <rjw@...ysocki.net>:
> > 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).
> >
> 
> I first tried the merge but git said I'm already uptodate (my tree
> is at 1a1891d Merge tag 'for-f2fs-4.9-rc2' of
> git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs already)
> 
> Then I did the revert of 899bb6642f2a and
> that worked fine for me.

OK, thanks!

Pointer arithmetics is messed up in that commit somewhat which may be the
reason for what you see.

Please check if this patch helps (instead of the revert):

https://patchwork.kernel.org/patch/9379639/

Thanks,
Rafael