linux-kernel - Re: [RFC PATCH 0/2] perf_events: add support for per-cpu per-cgroup monitoring (v3)

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Date:	Wed, 22 Sep 2010 12:26:20 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	balbir@...ux.vnet.ibm.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>, Li Zefan <lizf@...fujitsu.com>
Subject: Re: [RFC PATCH 0/2] perf_events: add support for per-cpu per-cgroup
 monitoring (v3)

Hi,

Ok, early testing shows that this seems to be working fine with the
pid approach.
Of course it is less convenient than just opening a file descriptor in
cgroup_fs.
There is more bookkeeping involved, incl. cleanup the child on exit.

The other thing is related to how to indicate we want cgroup and not per-thread.
For now, my patch is using a new attr.cgroup bit. The alternative is to use a
bit in the flags parameter to the syscall.

On Wed, Sep 22, 2010 at 11:18 AM, Balbir Singh
<balbir@...ux.vnet.ibm.com> wrote:
> * Peter Zijlstra <peterz@...radead.org> [2010-09-22 09:27:59]:
>
>> On Wed, 2010-09-22 at 09:53 +0530, Balbir Singh wrote:
>> > Yes, a task can belong to multiple subsystems, hence multiple cgroups.
>> > Ideally we'd want to use pid + subsystem
>>
>> Apparently we create a perf subsystem, and we only care about that. So
>> pid will uniquely identify a cgroup, since for each subsystem a task can
>> only belong to one cgroup.
>
> Hmm.. I misread the intention to mean we care about monitoring all
> data and aggregate it for each cgroup.
>
>>
>> > > One thing we could do is pass this cgroup identifier in the pid field
>> > > and use PERF_FLAG_CGROUP or something. Currently the syscall signature
>> > > uses pid_t, but I think we can safely change that to int.
>> >
>> > Or union it and overload the field to contain either pid_t or fd of the cgroup
>>
>> Its not a field, its an argument.
>
> Thanks!
>
> --
>        Three Cheers,
>        Balbir
>
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