linux-kernel - Re: [PATCH V11 09/15] perf: make events stream always parsable

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Message-ID: <CABPqkBRDB6_HvBAYNsZu2=VDhqYuzmYym97T7zWdvAVjuQgQQg@mail.gmail.com>
Date:	Wed, 21 Aug 2013 15:39:55 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH V11 09/15] perf: make events stream always parsable

On Wed, Aug 14, 2013 at 3:00 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 14/08/13 15:48, Adrian Hunter wrote:
>> The event stream is not always parsable because the format of a sample
>> is dependent on the sample_type of the selected event.  When there
>> is more than one selected event and the sample_types are not the
>> same then parsing becomes problematic.  A sample can be matched to its
>> selected event using the ID that is allocated when the event is opened.
>> Unfortunately, to get the ID from the sample means first parsing it.
>>
>> This patch adds a new sample format bit PERF_SAMPLE_IDENTIFER that puts
>> the ID at a fixed position so that the ID can be retrieved without
>> parsing the sample.  For sample events, that is the first position
>> immediately after the header.  For non-sample events, that is the last
>> position.
>>
>> In this respect parsing samples requires that the sample_type and ID
>> values are recorded.  For example, perf tools records struct perf_event_attr
>> and the IDs within the perf.data file.  Those must be read first
>> before it is possible to parse samples found later in the perf.data file.
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>
> Forgot to add Peter's ack which is here:
>
>         http://marc.info/?l=linux-kernel&m=137629757013526&w=2

Tested this patch via libpfm4 and per-event branch-stack.
Works well.

Tested-by: Stephane Eranian <eranian@...gle.com>
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