linux-kernel - Re: [PATCHv3 0/3] perf tool: Add new event group management

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Date:	Thu, 5 Jul 2012 18:15:20 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Namhyung Kim <namhyung@...il.com>, acme@...hat.com,
	a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	andi@...stfloor.org, drepper@...il.com
Subject: Re: [PATCHv3 0/3] perf tool: Add new event group management

On Mon, Jul 2, 2012 at 3:33 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> On Mon, Jul 02, 2012 at 10:11:02PM +0900, Namhyung Kim wrote:
>> 2012-07-02 (월), 12:15 +0200, Jiri Olsa:
>> > On Mon, Jul 02, 2012 at 10:53:44AM +0900, Namhyung Kim wrote:
>> > > Just a question, is there a way to know about the grouping at perf
>> > > report time?
>> >
>> > nope, AFAIK only ID and perf_event_attr is stored for event
>> > grouping is known only for record time
>> >
>>
>> I heard that Arnaldo (or Stephane) wanted to make perf report
>> group-aware or such so that it can show related events together. But to
>> do that, it seems we need to change the data file format first, right?
>>
>> Any idea?
>
> The next change I'm working on is to record and report
> PERF_FORMAT_GROUP related data. Here's commit comment
> from my next patchset:
>
> ---
> perf, tool: Enable sampling on specified event group leader
>
> Adding the functionality to the group modifier event syntax.
> Allowing user to select leader event inside the group using
> event index (command line event position in the group).
>
> Following example selects e2 as leader:
>   -e '{e1,e2,e3,e4}:2'
>
I don't understand why you actually need the :2 suffix. There can
only be one leader. So assume it is the first one. Users have to
know the first one is the leader which seems like a natural thing
to do for me. It would make you syntax less ugly than it already
is.

I would have thought you could enable this with a simple
cmdline option which changes the way you interpret the
multiple -e options:

perf record --group-reads -e e1,e2,e3 -e e4,e5,e6 .....

Would setup the group leaders (e1, e4) for 2 groups.
NO curly braces, no : needed.

> The selected event becomes group leader and is the only one
> doing samples.
>
> The rest of the events in the group are being read on each leader
> event sample by PERF_SAMPLE_READ sample type processing.
>
> Following example:
>   perf record -e {cycles,faults}:1 ls
>
>   - creates a group with 'cycles' and 'faults' events
>   - 'cycles' event is group leader and has sampling enabled
>   - 'faults' event is read each time 'cycles' sample,
>     the 'faults' count is attached to the 'cycles sample
>     via PERF_SAMPLE_READ sample type.
> ---
>
> The report does not need any new metadata about grouping, because
> the samples are generated/stored only from the group leader. The
> other events data are read from the PERF_FORMAT_GROUP leader sample
> data.
>
> So no data file format change for my next changes, but I'm not sure
> this is the report change you mean.
>
> jirka
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