linux-kernel - Re: perf_counters issue with enable_on

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Message-ID: <7c86c4470908241530r21804dbfqed2a218c3275ced5@mail.gmail.com>
Date:	Tue, 25 Aug 2009 00:30:56 +0200
From:	stephane eranian <eranian@...glemail.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>,
	Andi Kleen <andi@...stfloor.org>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <cel@...ibm.com>,
	Corey J Ashford <cjashfor@...ibm.com>,
	Philip Mucci <mucci@...s.utk.edu>,
	Dan Terpstra <terpstra@...s.utk.edu>,
	perfmon2-devel <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: perf_counters issue with enable_on_exec

On Mon, Aug 24, 2009 at 11:35 PM, Paul Mackerras<paulus@...ba.org> wrote:
> stephane eranian writes:
>
>> I am running into an issue trying to use enable_on_exec
>> in per-thread mode with an event group.
>>
>> My understanding is that enable_on_exec allows activation
>> of an event on first exec. This is useful for tools monitoring
>> other tasks and which you invoke as: tool my_program. In
>> other words, the tool forks+execs my_program. This option
>> allows developers to setup the events after the fork (to get
>> the pid) but before the exec(). Only execution after the exec
>> is monitored. This alleviates the need to use the
>> ptrace(PTRACE_TRACEME) call.
>>
>> My understanding is that an event group is scheduled only
>> if all events in the group are active (disabled=0). Thus, one
>
> Not quite - if the leader is disabled then none of the group goes on.
> If the leader is enabled then it and any other group members that are
> enabled go on.  If a non-leader member is disabled then it doesn't go
> on but it doesn't stop other members from going on.
>
okay, what is not clear to me is why you need that level of granularity?
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