linux-kernel - Re: [PATCH 1/2] perf_events: add cgroup support (v8)

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Message-ID: <AANLkTimPGpg13BbwHQCFF0yqSH01d+UUcutnNo9WCYp9@mail.gmail.com>
Date:	Fri, 11 Feb 2011 10:56:28 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com,
	robert.richter@....com, acme@...hat.com,
	Paul Menage <menage@...gle.com>
Subject: Re: [PATCH 1/2] perf_events: add cgroup support (v8)

Li,

On Fri, Feb 11, 2011 at 1:55 AM, Li Zefan <lizf@...fujitsu.com> wrote:
>>>> while there is already cgroup monitoring active. In that case and if we do not
>>>> want to wait until there is at least one ctxsw on all CPUs, then we have to
>>>> check if the other threads are not already running on the other CPUs.If so,
>>>> we need to do a cgroup switch on those CPUs. Otherwise, we have nothing to
>>>> do. Am I getting this right?
>>>
>>> Right, so if any of those tasks is currently running, that cpu will be
>>> monitoring their old cgroup, hence we send an IPI to flip cgroups.
>>>
>> I have built a test case where this would trigger. I launched a multi-threaded
>> app, and then I move the pid into a cgroup via: echo PID >/cgroup/tests/tasks.
>> I don't see any perf_cgroup move beyond the PID passed.
>>
>> I looked at kernel/cgroup.c and I could not find a invocation of
>> ss->attach() that
>> would pass threadgroup = true. So I am confused here.
>>
>> I wonder how the cgroupfs 'echo PID >tasks' interface would make the distinction
>> between PID and TID. It seems possible to move one thread of a multi-threaded
>> process into a cgroup but not the others.
>>
>
> You can do this:
>
>        # echo PID > cgroup.procs
>
> When the patchset that implements the above feature is accepted. See:
>
>        https://lkml.org/lkml/2011/2/7/418
>
> The below commit that confused you is actually a part of the above patchset,
> but it sneaked into the kernel accidentally:
>
> commit be367d09927023d081f9199665c8500f69f14d22
> Author: Ben Blum <bblum@...gle.com>
> Date:   Wed Sep 23 15:56:31 2009 -0700
>
>    cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time
>
Ok, that makes more sense now. I wil try with the above patchset applied to
verify this work as expected.
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