linux-kernel - Re: disabling group leader perf

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Date:	Mon, 06 Sep 2010 09:16:27 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	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

Sorry for top post, sending via my android phone. Today's a US holiday.


We can filter before the work, if we expose the parameters. Currently we filter what goes into the buffer and there are several cases where we don't know the result before the work.

If we also expose the parameters of a TRACE_EVENT, then we can filter on them before the work.

-- Steve

"Ingo Molnar" <mingo@...e.hu> wrote:

>
>* 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

-- 
Sent from my Android phone with K-9 Mail. Please excuse my brevity.
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