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

From: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>, Nikolay Borisov <kernel@kyup.com>
Cc: linux-kernel@vger.kernel.org, rostedt@goodmis.org,
	mingo@redhat.com, paulus@samba.org, acme@kernel.org,
	ebiederm@xmission.com, 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 21:49:48 +0530	[thread overview]
Message-ID: <578518A4.80301@linux.vnet.ibm.com> (raw)
In-Reply-To: <20160712130430.GQ30909@twins.programming.kicks-ass.net>

On Tuesday 12 July 2016 06:34 PM, Peter Zijlstra wrote:
> 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?

No need to create cgroup and confine processes to that cgroup. The below
check during event filtering will take care:

+	if (cpuctx->perf_ns != event->perf_ns)
+		return false;

event->perf_ns is set during perf_event_alloc():

+	if (current->nsproxy->perf_ns != &init_perf_ns) {
+		/*
+		 * If we are called from our own perf namespace, set
+		 * event->perf_ns
+		 */
+		event->perf_ns = current->nsproxy->perf_ns;
+		[...]
+	}

> 
>> 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.
> 

-- 
Regards,
Aravinda