linux-kernel - Re: [PATCH 04/11] perf: Make perf_cgroup_from

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Message-ID: <20141008102758.GN14343@console-pimps.org>
Date:	Wed, 8 Oct 2014 11:27:58 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 04/11] perf: Make perf_cgroup_from_task() global

On Tue, 07 Oct, at 08:51:57PM, Peter Zijlstra wrote:
> On Wed, Sep 24, 2014 at 03:04:08PM +0100, Matt Fleming wrote:
> > From: Matt Fleming <matt.fleming@...el.com>
> > 
> > Move perf_cgroup_from_task() from kernel/events to include/ along with
> > the necessary struct definitions, so that it can be used by the PMU
> > code.
> > 
> > The upcoming Intel Cache Monitoring PMU driver assigns monitoring IDs
> > based on a task's association with a cgroup - all tasks in the same
> > cgroup share an ID. We can use perf_cgroup_from_task() to track this
> > association.
> 
> Not yet having read the rest of the patches and maybe understanding
> things wrong, that doesn't sound right.
> 
> The RMID should be associated with events, not groups. The event can be
> associated with whatever perf provides {task, cgroup, cpu}.

I think I just wrote the commit message in a goofy way.

What we actually use perf_cgroup_from_task() for is to figure out when
to prohibit an event from being created if it overlaps/conflicts with an
existing event.

I'll rewrite the commit message to be clearer.

-- 
Matt Fleming, Intel Open Source Technology Center
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