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

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Message-ID: <20140908133428.GG6758@twins.programming.kicks-ass.net>
Date:	Mon, 8 Sep 2014 15:34:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
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 02:01:41PM +0200, Jiri Olsa wrote:
> 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

Urgh, see I knew I was missing something.

Can't we fix that? Lemme check to see what relies on this.

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