linux-kernel - Re: [PATCH 1/9] perf: Remove redundant parent context check from context

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Date:	Mon, 8 Sep 2014 14:01:41 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Jen-Cheng(Tommy) Huang" <tommy24@...ech.edu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/9] perf: Remove redundant parent context check from
 context_equiv

On Mon, Sep 08, 2014 at 12:01:22PM +0200, Peter Zijlstra wrote:
> On Mon, Sep 08, 2014 at 11:48:55AM +0200, Peter Zijlstra wrote:
> 
> > > The thing is; I don't understand those reasons. That commit log doesn't
> > > explain.
> > 
> > Ah wait, I finally see. I think we want to fix that exit path, not
> > disallow the cloning.
> > 
> > The thing is, by not allowing this optimization simple things like eg.
> > pipe-test say very expensive.
> 
> So its 179033b3e064 ("perf: Add PERF_EVENT_STATE_EXIT state for events
> with exited task") that introduces the problem. Before that things would
> work correctly afaict.

hum, I dont think so.. because the perf_remove_from_context set event
to PERF_EVENT_STATE_OFF state anyway.. thus making any new cloned events
disabled

the PERF_EVENT_STATE_EXIT should be just notification for poll to return HUP

> The exit would remove from the context but leave the event in existence.
> Both the fd and the inherited events would have references to it, only
> once those are gone do we destroy the actual event.
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