linux-kernel - Re: [PATCH 2/5] perf: Destroy event's children on task exit

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Message-ID: <20140711132309.GH20603@laptop.programming.kicks-ass.net>
Date:	Fri, 11 Jul 2014 15:23:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
	Alexander Yarygin <yarygin@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 2/5] perf: Destroy event's children on task exit

On Fri, Jul 11, 2014 at 01:56:19PM +0200, Jiri Olsa wrote:
> From: Jiri Olsa <jolsa@...hat.com>
> 
> When task exits we close:
>   1) all events that are installed in task
>   2) all events owned by task (via file descriptor)
> 
> But we don't close children events of 2) events. Those children
> events stay until the child task exits and are useless with the
> parent being gone, because we have no way to get to values any
> more.
> 
> Plus if the event stays installed in task even with the owner task
> gone, it runs the perf callback any time the task forks, for no
> real reason.
> 
> Closing all children events events when the owner task of the
> parent event is closed.

So I _think_ the reason we didn't do this is because this is potentially
very expensive and keeping them around isn't too much bother, they'll
die eventually.

But I can't really remember. Ingo any recollections / opinions?
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