linux-kernel - Re: [perf tool] cgroup support broken on Debian?

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Date:	Tue, 16 Dec 2014 12:29:35 -0500
From:	Stephane Eranian <eranian@...gle.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Stephane Eranian <eranian@...il.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>
Subject: Re: [perf tool] cgroup support broken on Debian?

Vince,

On Tue, Dec 16, 2014 at 12:17 PM, Vince Weaver <vincent.weaver@...ne.edu> wrote:
> On Mon, 15 Dec 2014, Stephane Eranian wrote:
>> On Mon, Dec 15, 2014 at 11:01 PM, Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:
>
>> fs is visible. The cgroup file system type is not there anymore. They are using
>> tmpfs which is not ideal to detect just cgroup. Looks like now, we have to look
>> at the mount point which is flaky.
>
> The trivial fix is to just always assume things will be under
>         /sys/fs/cgroup
> which looks like to be the new official mount point.
>
> This will break on older systems though, or systems that mount cgroupfs in
> multiple locations.
>
> Another alternative is to change the interface to require the full
> cgroupfs pathname as an argument to -G
>
That's not user friendly!
We need to detect where this is mounted to.
I think we can try the tmpfs mount points. Just need to then check if
a file entry
that can only exist for cgroups is there, such as cgroups.procs.

>> Yes, the error needs to be improved or even added. The following common
>> errors are encountered:
>>
>> - -G option requires -a (system-wide), otherwise it does not work at all
>> - -G option must always be specified AFTER the ALL event list
>> - -G and explicit event groups is not well supported by the tool yet.
>> An event group must have the same cgroup.
>> - Cgroups are specified per event
>> - -G cgroup order follows the event order: -e e1, e2, e3 -G g1,g2,g3:
>> g1->e1, g2->e2, g3->e3
>> - It is possible to indicate no cgroup with -G: -e e1,e2,e3 -G g1,,g3
>> using empty group (,,)
>
> I'll see if I can get a patch together that impements this.
>
> Vince
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