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

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Date:	Mon, 28 Dec 2009 15:02:12 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tim Blechmann <tim@...ngt.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: perf: counter and event question

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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