Message-ID: <4B38A707.4060904@klingt.org>
Date: Mon, 28 Dec 2009 13:39:35 +0100
From: Tim Blechmann <tim@klingt.org>
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To: Peter Zijlstra <peterz@infradead.org>
CC: linux-kernel@vger.kernel.org
Subject: Re: perf: counter and event question
References: <4B389391.8050303@klingt.org> <1261999573.7135.83.camel@laptop>
In-Reply-To: <1261999573.7135.83.camel@laptop>
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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?=20
>=20
> 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

--=20
tim@klingt.org
http://tim.klingt.org

art is short - life is long
  Jack Kerouac


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