linux-kernel - Re: [patch] Performance Counters for Linux, v2

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Message-ID: <493EAC45.4050704@nortel.com>
Date:	Tue, 09 Dec 2008 11:35:01 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Will Newton <will.newton@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, eranian@...il.com,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Veen <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Miller <davem@...emloft.net>,
	Paul Mackerras <paulus@...ba.org>,
	Paolo Ciarrocchi <paolo.ciarrocchi@...il.com>
Subject: Re: [patch] Performance Counters for Linux, v2

Will Newton wrote:
> On Tue, Dec 9, 2008 at 1:46 PM, Ingo Molnar <mingo@...e.hu> wrote:
> 
>> Firstly, sampling "at 1msec intervals" or any fixed period is a _very_
>> wrong mindset - and cross-sampling counters is a similarly wrong mindset.
> 
> If your hardware does not interrupt on overflow I don't think you have
> any choice in the matter. I know such hardware is less than ideal but
> it exists so it should be supported.

I think you could still set up the counters as Ingo describes and then 
sample the counters (as opposed to the program) at a suitable interval 
(chosen such that the counters won't overflow more than once between 
samples).

Chris
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