linux-kernel - Re: [RFC PATCH] perf: Container-aware tracing support

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Message-ID: <20150717101950.GS3644@twins.programming.kicks-ass.net>
Date:	Fri, 17 Jul 2015 12:19:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Aravinda Prasad <aravinda@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	mingo@...hat.com, paulus@...ba.org, acme@...nel.org,
	hbathini@...ux.vnet.ibm.com, ananth@...ibm.com
Subject: Re: [RFC PATCH] perf: Container-aware tracing support

On Wed, Jul 15, 2015 at 09:51:52PM +0530, Aravinda Prasad wrote:
> >> +	} else if (task_active_pid_ns(current) != &init_pid_ns) {
> > 
> > Why the pid namespace?
> 
> This comes from my understanding of container -- having at least a
> separate PID namespace with processes inside a container grouped into a
> single perf_event cgroups subsystem.
> 
> I know there are other ways to define a container, however, I thought I
> start with the above one.

Right, but you should at least mention this, preferably in a comment.

> > 
> >> +		/* Don't set event->cgrp if task belongs to root cgroup */
> >> +		if (task_css_is_root(current, perf_event_cgrp_id))
> >> +			return ret;
> > 
> > So if you have the root perf_cgroup inside your container you can
> > escape?
> 
> If we have root perf_cgroup inside the container then even if we set
> event->cgrp we will be including all processes in the system.

Yes, that's what I said. Why does that make sense?
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