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

[Sedat Dilek]

On Thu, Oct 20, 2016 at 4:32 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> wrote:
>> >> > On Wednesday, October 19, 2016 06:59:35 PM JÃrg Otte wrote:
>> >> >> 2016-10-19 17:29 GMT+02:00 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>:
>> >> >> > On Wed, Oct 19, 2016 at 4:07 AM, JÃrg Otte <jrg.otte@xxxxxxxxx> 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 JÃrg.
>>
>> 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@xxxxxxxxxxxxxxx> # 4.8+
>
> The commit in question might not make it into 4.8.y yet.
>

For all followers...

The fix is now in Linus tree (see [1]).

- Sedat -

[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6fe46a79ecd79606bb96fada4515f6b23f87b62