Subject: Re: perf: counter and event question
From: Peter Zijlstra <peterz@infradead.org>
To: Tim Blechmann <tim@klingt.org>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <4B38AE1D.8060703@klingt.org>
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	 <4B38AE1D.8060703@klingt.org>
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Date: Mon, 28 Dec 2009 15:02:12 +0100
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On Mon, 2009-12-28 at 14:09 +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 ...
> > 
> > Large number of samples and sample interval are only related through the
> > runtime of your application.
> > 
> > Use a sensible period (~10k ins) and run a 'little' longer.
> 
> well, for my application, i am not interested in statistical data, but
> in the order of the events ...
> (i am not doing profiling, but trying to gather a sequence of
> machine-structured data for an artistic project)

Well, then use the branch tracer, that will give you the relation
between blocks of code and is actually doable.

But I guess you could hack out the throttle and run the cycle counter
with period=1 for userspace only.

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