linux-kernel - Re: perf: counter and event question

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Message-ID: <4B38A707.4060904@klingt.org>
Date:	Mon, 28 Dec 2009 13:39:35 +0100
From:	Tim Blechmann <tim@...ngt.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: perf: counter and event question

On 12/28/2009 12:26 PM, Peter Zijlstra wrote:
> On Mon, 2009-12-28 at 12:16 +0100, Tim Blechmann wrote:
>> like it is impossible to sample instructions with a period of 1? 
> 
> Pretty much, imagine the cpu getting a trap every cycle.

is this a hardware restriction? a slowdown is acceptable for me, as long
as i am able to collect a huge number of samples accurately ...

> In order to avoid the machine grinding to a halt, we've implemented a
> throttle which defaults to 100k samples/s, anything over that will be
> discarted.

i just found the proc interface for perf_event_max_sample_rate ... it
would be nice to have a short section on the event throttling in
tools/perf/design.txt ...

thanks, tim

-- 
tim@...ngt.org
http://tim.klingt.org

art is short - life is long
  Jack Kerouac


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