linux-kernel - Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes

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Date:   Fri, 7 Oct 2016 13:37:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Joseph Salisbury <joseph.salisbury@...onical.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes

On Fri, Oct 7, 2016 at 1:22 PM, Joseph Salisbury
<joseph.salisbury@...onical.com> wrote:
>
> Yes, CONFIG_SCHED_AUTOGROUP is enabled in the Ubuntu kernel.  However,
> that config was also enable in the Ubuntu 4.4 kerrnels without seeing
> this issue.   I can try disabling the config in the 4.8 based kernel and
> see if that changes things.

No, that wouldn't make any sense. I just wanted to know that the
option was enabled, because that option really *should* help buffer
other processes from one session that is a CPU hog.

So something is seriously wrong in that situation if other things get
very choppy. Of course, the fact that it apparently happens on one
particular machine only means that it's hard to figure out what
triggers it. Maybe some unlucky combination of cpufreq and thermal
throttling by the hardware, coupled with the scheduler change.

Peter?

                 Linus