Date: Thu, 04 Dec 2008 23:52:38 -0800 (PST)
Message-Id: <20081204.235238.229578299.davem@davemloft.net>
To: arjan@infradead.org
Cc: mingo@elte.hu, paulus@samba.org, tglx@linutronix.de,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
       akpm@linux-foundation.org, eranian@googlemail.com, dada1@cosmosbay.com,
       robert.richter@amd.com, hpa@zytor.com, a.p.zijlstra@chello.nl,
       rostedt@goodmis.org
Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux
From: David Miller <davem@davemloft.net>
In-Reply-To: <20081204230206.6e083d51@infradead.org>
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	<20081205063131.GB12785@elte.hu>
	<20081204230206.6e083d51@infradead.org>
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From: Arjan van de Ven <arjan@infradead.org>
Date: Thu, 4 Dec 2008 23:02:06 -0800

> On Fri, 5 Dec 2008 07:31:31 +0100
> Ingo Molnar <mingo@elte.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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