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

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Date:	Tue, 9 Dec 2008 20:02:54 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	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


* Chris Friesen <cfriesen@...tel.com> wrote:

> Ingo Molnar wrote:
>
>> When there are two (or more) hw metrics to profile, the ideally best 
>> (i.e. the statistically most stable and most relevant) sampling for 
>> the two statistical variables (say of l2_misses versus l2_accesses) is 
>> to sample them independently, via their own metric. Not via a static 
>> 1khz rate - or via picking one of the variables to generate samples.
>
> Regardless of sampling method, don't you still want some way to 
> enable/disable the various counters as close to simultaneously as 
> possible?

If it's about counter control for the monitored task, then we sure could 
do something about that. (apps/libraries could thus select a subset of 
functions to profile/measure, runtime, etc.)

If it's about counter control for the profiler/debugger, i'm not sure how 
useful that is - do you have a good usecase for it?

	Ingo
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