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

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Message-ID: <20161008080019.GE3142@twins.programming.kicks-ass.net>
Date:   Sat, 8 Oct 2016 10:00:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joseph Salisbury <joseph.salisbury@...onical.com>
Cc:     torvalds@...ux-foundation.org, efault@....de, tglx@...utronix.de,
        LKML <linux-kernel@...r.kernel.org>, mingo@...nel.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes

On Fri, Oct 07, 2016 at 03:38:23PM -0400, Joseph Salisbury wrote:
> Hello Peter,
> 
> A kernel bug report was opened against Ubuntu [0].  After a kernel
> bisect, it was found that reverting the following commit resolved this bug:
> 
> commit 3d30544f02120b884bba2a9466c87dba980e3be5
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Tue Jun 21 14:27:50 2016 +0200
> 
>     sched/fair: Apply more PELT fixes

That commit doesn't revert cleanly, did you take out more?

> The regression was introduced as of v4.8-rc1.  The bug can be reproduced
> on an X1 Carbon with the following:
> stress -c $your_total_cpu_cores
> 
> I was hoping to get your feedback, since you are the patch author.  Do
> you think gathering any additional data will help diagnose this issue,
> or would it be best to submit a revert request? 

I'll try and have a look asap, but I'm traveling next week so it might a
tad slower than normal.

If you could provide a /proc/sched_debug dump while the thing is running
that'd might be useful.

Thanks!