Re: [RFC PATCH 2/2] perf: Filter events based on perf-namespace

From: Nikolay Borisov
Date: Tue Jul 12 2016 - 08:41:51 EST

On 07/12/2016 02:47 PM, Peter Zijlstra wrote:
> On Tue, Jul 12, 2016 at 02:56:17PM +0530, Aravinda Prasad wrote:
>> On Monday 27 June 2016 09:20 PM, Peter Zijlstra wrote:
>>> On Tue, Jun 14, 2016 at 10:19:51PM +0530, Aravinda Prasad wrote:
>>>> Whenever perf tool is executed inside a container, this
>>>> patch restricts the events to the perf-namespace in which
>>>> the perf tool is executing.
>>>> This patch is based on the existing support available
>>>> for tracing with cgroups.
>>>> TODO:
>>>> - Avoid code duplication.
>>> Can't you, at perf_event_open() time, convert a per-cpu event into a
>>> per-cpu-per-cgroup event for these namespace thingies?
>>> That seems to immediately and completely remove all that duplication.
>> Sorry for the delay in the response.
>> I was looking into a way how a per-cpu event can be converted to
>> per-cpu-per-cgroup event at perf_event_open() but could not figure out
>> how to do this conversion. The cgroup event expects the fd of the cgroup
>> directory in cgroupfs and in this case we don't have any fd passed in.
>> Not sure if I am missing anything.
> Would not the current namespace have a link to the correct cgroup?
> Wasn't that the entire point of the namespace thing?

Namespaces and cgroups are completely orthogonal to one another. Also in
the v1 of cgroups it's possible to have a process member of more than 1