linux-kernel - Re: perf_counters issue with self-sampling threads

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Message-Id: <1248713801.6987.1684.camel@twins>
Date:	Mon, 27 Jul 2009 18:56:41 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	eranian@...il.com
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Robert Richter <robert.richter@....com>,
	Paul Mackerras <paulus@...ba.org>,
	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 self-sampling threads

On Mon, 2009-07-27 at 18:51 +0200, stephane eranian wrote:
> Hi,
> 
> I believe there is a problem with the current perf_counters (PCL)
> code for self-sampling threads. The problem is related to sample
> notifications via signal.
> 
> PCL (just like perfmon) is using SIGIO, an asynchronous signal,
> to notify user applications of the availability of data in the event
> buffer.
> 
> POSIX does not mandate that asynchronous signals be delivered
> to the thread in which they originated. Any thread in the process
> may process the signal, assuming it does not have the signal
> blocked.

Bugger, you're right. /me kicks POSIX again for creating these crazy ass
semantics.

I'll look at fixing this.

Thanks!

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