linux-kernel - Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and SPECjvm2008 benchmarks against 4.6 kernel

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Message-ID: <CAE4VaGBzNyhw58cASkQofCVaUHPUYrJ97_U8ymHMw7A9_0mjsg@mail.gmail.com>
Date:	Fri, 24 Jun 2016 09:44:41 +0200
From:	Jirka Hladky <jhladky@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Kamil Kolakowski <kkolakow@...hat.com>
Subject: Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and
 SPECjvm2008 benchmarks against 4.6 kernel

Hi Peter,

thanks a lot for looking into it!

I have tried to disable autogroups

sysctl -w kernel.sched_autogroup_enabled=0

and I can confirm that performance is then back at level as in 4.6 kernel.

I have double checked default settings and

kernel.sched_autogroup_enabled

is by default ON both in 4.6 and 4.7 kernel.

Jirka

On Thu, Jun 23, 2016 at 8:43 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Jun 23, 2016 at 08:33:18PM +0200, Peter Zijlstra wrote:
>> On Fri, Jun 17, 2016 at 01:04:23AM +0200, Jirka Hladky wrote:
>>
>> > > What kind of config and userspace setup? Do you run this cruft in a
>> > > cgroup of sorts?
>> >
>> >  No, we don't do any special setup except to control the number of threads.
>>
>> OK, so I'm fairly certain you _do_ run in a cgroup, because its made
>> almost impossible not to these days.
>>
>> Run:
>>
>>       grep java /proc/sched_debug
>>
>> while the thing is running. That'll show you the actual cgroup the stuff
>> is running in.
>
> That'll end up looking something like:
>
> root@...-ep:/usr/src/linux-2.6# grep java /proc/sched_debug
>             java  2714     18270.634925        89   120         0.000000         1.490023         0.000000 0 0 /user.slice/user-0.slice/session-2.scope
>             java  2666     18643.629673         2   120         0.000000         0.063129         0.000000 0 0 /user.slice/user-0.slice/session-2.scope
>             java  2676     18655.652878         3   120         0.000000         0.077127         0.000000 0 0 /user.slice/user-0.slice/session-2.scope
>             java  2680     18655.683384         3   120         0.000000         0.082993         0.000000 0 0 /user.slice/user-0.slice/session-2.scope
>
> which shows a 3 deep hierarchy. Clearly these people haven't the
> faintest clue about the cost of what they're doing. This stuff ain't
> free.
>
>