linux-kernel - Re: [PATCH -tip v2 2/6] perf bts: Introduce new sub command 'perf bts trace'

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Date:	Fri, 24 Dec 2010 19:04:23 +0900
From:	Akihiro Nagai <akihiro.nagai.hw@...achi.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	2nddept-manager@....hitachi.co.jp,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH -tip v2 2/6] perf bts: Introduce new sub command 'perf
 bts trace'

(2010/12/22 3:31), Frederic Weisbecker wrote:
[...]
>> +static int process_sample_event(event_t *event __unused,
>> +	struct sample_data *sample, struct perf_session *session __unused)
>> +{
>> +	/* sample->ip is 'from address', sample->addr is 'to address' */
>> +	printf(FMT_ADDR " =>  " FMT_ADDR "\n", sample->ip, sample->addr);
>
> It seems this unconditionally prints out the event, but a sample
> event can be about anything. If you recorded only branches it's fine,
> but if there were other events this will mess up.
Exactly.
I'll add a check code of PERF_SAMPLE_ID there.


And, I found the problem that perf cannot handle the data including
multiple event types. I executed following command to make perf.data
includes two event types: hardware and software event.

  # perf record -e branches:u -c 1 -d -e raw_syscalls:sys_enter ls
  (... ls outputs)
[ perf record: Woken up 18 times to write data ]
[ perf record: Captured and wrote 4.468 MB perf.data (~195216 samples) ]

  # perf bts trace
   Fatal: non matching sample_type

It results in error. Other perf subcommands also failed on this recorded data.
For example, perf annotate, perf script, perf report.

In the future, I would like to analyze BTS log and other type events
at the same time.

>
> Well, when you launch the tool you can iterate into the session->header.attr
> and check if there is something else than a branch perf event. And then emit
> a warning if so.
>
> That doesn't solve the problem but the user will know there is one.
>
> Actually the best would be to select PERF_SAMPLE_ID in the sample_type
> on record and also PERF_FORMAT_ID in the read_format.
>
> Then you can find the PERF_SAMPLE_ID that matches your event. If we
> record that in the perf headers we can retrieve which events id are the
> branch ones.
Agreed.

>
> But well, that's a secondary problem for now.
Thank you for your advise!

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Akihiro Nagai
Email: akihiro.nagai.hw@...achi.com
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