linux-kernel - Re: [PATCH] perf tools: Exit recording if events have non matching sample type

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Date:	Thu, 29 Sep 2011 23:21:34 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	Jiri Olsa <jolsa@...hat.com>, a.p.zijlstra@...llo.nl,
	mingo@...e.hu, Stephane Eranian <eranian@...gle.com>,
	paulus@...ba.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tools: Exit recording if events have non matching
 sample type

Em Thu, Sep 29, 2011 at 06:58:20PM -0600, David Ahern escreveu:
> On 09/29/2011 06:40 PM, Arnaldo Carvalho de Melo wrote:
> > This comes from time to time:
> > 
> > http://us.generation-nt.com/answer/bug-perf-event-sampling-buffer-format-cannot-handle-multi-event-sampling-help-202985832.html
> > 
> > The whole point of sample_type is to ask for just what is needed for
> > some specific event so that we reduce the per sample footprint.
> > 
> > So we allow for multiple types of events to be on the same stream, but
> > not for them to have just what each need, its a limitation, one that we
> > can solve. I see no reason not to solve it :-)
> > 
> > The evsel/evlist classes were designed to abstract away such details,
> > i.e. perf_evlist__mmap should notice different sample_types and sort
> > this out transparently.
> > 
> > And then perf_evlist__mmap_read(evlist, idx), evlist->nr_mmaps should be
> > enough to process the events :-)
> > 
> > - Arnaldo
> 
> An ABI change fixes the root cause of the current problem -- put an id
> in perf_event_header. The id maps to the evsel which has the
> sample_type. Right now you have to parse the sample to get the id to get
> the evsel.

This id is not always needed, so it shouldn't go to perf_event_header.
Peter, can you comment here? ;-)

- Arnaldo
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