linux-kernel - Re: [patch 0/3] [Announcement] Performance Counters for Linux

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Message-Id: <20081204.235238.229578299.davem@davemloft.net>
Date:	Thu, 04 Dec 2008 23:52:38 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	arjan@...radead.org
Cc:	mingo@...e.hu, paulus@...ba.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	akpm@...ux-foundation.org, eranian@...glemail.com,
	dada1@...mosbay.com, robert.richter@....com, hpa@...or.com,
	a.p.zijlstra@...llo.nl, rostedt@...dmis.org
Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux

From: Arjan van de Ven <arjan@...radead.org>
Date: Thu, 4 Dec 2008 23:02:06 -0800

> On Fri, 5 Dec 2008 07:31:31 +0100
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > Btw., i'm curious, why would we want to do that? It skews the results
> > if the task continues executing and counters stop. To get the highest 
> > quality profiling output the counters should follow the true state of
> > the task that is profiled - and events should be passed to the
> > monitoring task asynchronously. The _events_ can contain precise
> > coupled information 
> > - but the counters should continue.
> 
> btw stopping the task on counter overflow is an issue for things that
> want to self profile, like JITs

They can fork off a thread to do this.

No blocking on couter overflow leads to inaccurate results.
This is a pretty fundamental aspect of perf counter usage.
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