linux-kernel - Re: [PATCH V2 0/7] sched/deadline: fix cpusets bandwidth accounting

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Date:   Fri, 2 Feb 2018 14:17:50 +0100
From:   Luca Abeni <luca.abeni@...tannapisa.it>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     peterz@...radead.org, lizefan@...wei.com, mingo@...hat.com,
        rostedt@...dmis.org, claudio@...dence.eu.com, bristot@...hat.com,
        tommaso.cucinotta@...tannapisa.it, juri.lelli@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 0/7] sched/deadline: fix cpusets bandwidth accounting

Hi Mathieu,

On Thu,  1 Feb 2018 09:51:02 -0700
Mathieu Poirier <mathieu.poirier@...aro.org> wrote:

> This is the follow-up patchset to [1] that attempt to fix a problem
> reported by Steve Rostedt [2] where DL bandwidth accounting is not
> recomputed after CPUset and CPU hotplug operations.  When CPU hotplug and
> some CUPset manipulation take place root domains are destroyed and new ones
> created, loosing at the same time DL accounting information pertaining to
> utilisation.  Please see [1] for a full description of the approach.

I do not know the cgroup / cpuset code too much, so I have no useful
comments on your patches... But I think this patchset is a nice
improvemnt respect to the current situation.

[...]
> A notable addition is patch 7/7 - it addresses a problem seen when hot
> plugging out a CPU where a DL task is running (see changelog for full
> details).  The issue is unrelated to this patchset and will manifest
> itself on a mainline kernel.

I think I introduced this bug with my reclaiming patches, so I am
interested.
When a cpu is hot-plugged out, which code in the kernel is responsible
for migrating the tasks that are executing on such CPU? I was sure I
was handling all the relevant codepaths, but this bug clearly shows
that I was wrong.


			Thanks,
				Luca