linux-kernel - Re: [patch 0/4] perf_counter tools: support annotation of live kernel modules

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Date:	Thu, 02 Jul 2009 09:55:42 +0200
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch 0/4] perf_counter tools: support annotation of live
 kernel modules

On Thu, 2009-07-02 at 09:42 +0200, Ingo Molnar wrote:

(squirrels suggestions away for later reference)

> Btw, another thing: we are thinking about making -F 1000 (1 KHz 
> auto-freq sampling) the default for perf top and perf record. This 
> way we'd always gather enough data (and never too much or too little 
> data), regardless of the intensity of the workload. Have you played 
> with -F before, what's your general experience about it? It's 
> particularly useful for 'rare' and highly fluctuating events like 
> cache-misses.
> 
> Maybe 1KHz is a bit too low - Oprofile defaults to 100000 cycles 
> interval by default which is about 10 KHz on a 1GHz box and 30 KHz 
> on a 3GHz box. Perhaps 10 KHz is a better default?

My default usage is 1000Hz to keep overhead low.  Works fine for me.

	-Mike

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