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

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Message-ID: <4E852C4D.4010307@gmail.com>
Date:	Thu, 29 Sep 2011 20:41:17 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
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

On 09/29/2011 08:21 PM, Arnaldo Carvalho de Melo wrote:
> 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? ;-)

I'm talking about a new 'id' that would always be needed *for samples*
-- it identifies the evsel it is associated with. The evsel has the
sample type. The sample_type is then used to parse it. Seems like a
simpler solution then having mmap's per sample type and then writing
separate files.

David
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