linux-kernel - Re: disabling group leader perf

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Message-ID: <20100906124046.GA20777@elte.hu>
Date:	Mon, 6 Sep 2010 14:40:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, linux-perf-users@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: disabling group leader perf_event


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, 2010-09-06 at 14:58 +0300, Avi Kivity wrote:
> > On 09/06/2010 02:54 PM, Peter Zijlstra wrote:
> > >
> > >> Basically, to read() all events in one go.  I have many of them.
> > >>
> > >> My current problem is that I have an event (kvm_exit) which I want to
> > >> drill down by looking at a field (exit_reason).  So I create lots of
> > >> separate perf_events with a filter for each reason:
> > >> kvm_exit(exit_reason==0), kvm_exit(exit_reason==1), etc.  But filters
> > >> are fairly slow (can have ~60 such events on AMD), so I want to make
> > >> this drill-down optional.
> > > Yeah, filters suck.
> > 
> > Any idea why?  I saw nothing obvious in the code, except that there 
> > is lots of it.
> 
> It filters after it does all the hard work of creating the trace 
> event, instead of before.

Btw., that's an implementational property of filters that would be nice 
to fix.

If it's not doable within CPP then outside of it.

	Ingo
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