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

From: ebiederm@xmission.com (Eric W. Biederman)
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nikolay Borisov <kernel@kyup.com>,
	Aravinda Prasad <aravinda@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org, rostedt@goodmis.org,
	mingo@redhat.com, paulus@samba.org, acme@kernel.org,
	hbathini@linux.vnet.ibm.com, ananth@in.ibm.com
Subject: Re: [RFC PATCH 2/2] perf: Filter events based on perf-namespace
Date: Tue, 12 Jul 2016 08:55:17 -0500	[thread overview]
Message-ID: <8737nf55bu.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20160712130430.GQ30909@twins.programming.kicks-ass.net> (Peter Zijlstra's message of "Tue, 12 Jul 2016 15:04:30 +0200")

Peter Zijlstra <peterz@infradead.org> writes:

> On Tue, Jul 12, 2016 at 03:41:42PM +0300, Nikolay Borisov wrote:
>
>> Namespaces and cgroups are completely orthogonal to one another. 
>
> Then how do you specify what your new 'root' is? Surely you must first
> create a cgroup and then confine yourself to that?
>
>> Also in the v1 of cgroups it's possible to have a process member of
>> more than 1 cgroup.
>
> Yeah, so? We only care about the perf controller obviously.

I completely misread the description of this, or I would have something
earlier.  For some reason I thought he was talking about the perf
controller.

As I recall the tricky part of this was to have tracing that was safe
and usable inside of a container.  If you can align a per cgroup with
your container that is probably sufficient for the select of processes.

At the same time there is a real desire to have identifiers like pids
translated into the appropriate form for inside of the container.
Without that translation they are meaningless inside a container.
Further it is necessary to be certain the trancing that is used is is
safe for unprivileged users.

I don't think I ever suggested or approved of the concept of a perf
namespace and that sounds a bit dubious to me.

Eric