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Date: Fri, 2 Sep 2016 15:59:36 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: ast@fb.com, lkml <linux-kernel@vger.kernel.org>, acme@kernel.org,
        alexander.shishkin@linux.intel.com, mingo@redhat.com,
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        ebiederm@xmission.com, sargun@sargun.me,
        Aravinda Prasad <aravinda@linux.vnet.ibm.com>,
        brendan.d.gregg@gmail.com
Subject: Re: [PATCH v2 1/2] perf: add container identifier entry in perf
 sample data
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On Fri, Sep 02, 2016 at 07:25:31PM +0530, Hari Bathini wrote:
> >I'm thinking this value is mostly the same for tasks, just like COMM and
> 
> I think so, too. Namespaces aren't changed that often for tasks...
> 
> >MMAP. Could we therefore not emit (sideband) events whenever a task
> >changes namespace and get the same information but with tons less data?
> 
> You mean, something like PERF_RECORD_NAMESPACE that
> emits events on fork, clone, setns..?

Yep.

> 
> >That also gives the possibility of recording all namespaces, not just
> >the one.
> 
> True. If we record all namespaces, container identifier interpretation
> can be left to the userspace to decide, which is much more flexible...

The only complication is initial state, on record start you'd have to
trawl /proc and generate 'fake' namespace records for all (relevant)
tasks.

We do the same with MMAP records, we parse /proc/$pid/maps for that.

Is this namespace stuff available in /proc somewhere?