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

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Message-ID: <57F80400.9040503@canonical.com>
Date:   Fri, 7 Oct 2016 16:22:24 -0400
From:   Joseph Salisbury <joseph.salisbury@...onical.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 10/07/2016 03:57 PM, Linus Torvalds wrote:
> On Fri, Oct 7, 2016 at 12:38 PM, Joseph Salisbury
> <joseph.salisbury@...onical.com> wrote:
>> A kernel bug report was opened against Ubuntu [0].  After a kernel
>> bisect, it was found that reverting the following commit resolved this bug:
> Hmm. Interesting, and it sounds like we should revert that unless
> somebody figures out *why* following the rules wrt cfq updates causes
> problems. But I also wonder what the Ubuntu kernel config is. Does
> Ubuntu enable CONFIG_SCHED_AUTOGROUP=y, for example? Because
> regardless of any other scheduler issues, autogrouping *should* mean
> that when you run some CPU hogger in one session, that should still
> balance all CPU time with other sessions..
>
> I'm not seeing anything odd on my xps13, which should have a similar
> CPU to the X1 Carbon.
>
>                Linus
Hi Linus,

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.

Thanks,

Joe