linux-kernel - Re: [PATCH 3/4] perf: teach perf inject to merge sched_stat_* and sched

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Date:	Mon, 27 Aug 2012 11:22:18 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 3/4] perf: teach perf inject to merge sched_stat_* and
 sched_switch events (v2)

2012/8/25 Frederic Weisbecker <fweisbec@...il.com>:
>> +     if (!strcmp(evname, "sched_switch") ||  sched_process_exit) {
>> +             list_for_each_entry(ent, &samples, node)
>> +                     if (sample->pid == ent->pid)
>
> I suspect what you're rather interested in is the sample tid.

Yes, you are right.

>
>> +
>> +     } else if (!strncmp(evname, "sched_stat_", 11)) {
>> +             u32 pid;
>> +
>> +             pid = raw_field_value(evsel->tp_format,
>> +                                     "pid", sample->raw_data);
>
> There you parse the pid from the trace content. That's fine because
> it's actually the tid that is saved on the trace event. But this one
> is not pid-namespace safe (it saves current->pid directly) while
> sample->tid is pid-namespace safe (it uses task_pid_nr_ns).
>
> So I suggest you to use sample->tid instead, plus that's going to be
> consistant with what you did above.

Here is a problem, because a pid from the trace content and
sample->tid are not the same.
A kernel wakes up a task1 and do it from a context of another task2.
In this case a pid from the trace content is a pid of the task1 and a
sample->tid is a pid of the task2.

DECLARE_EVENT_CLASS(sched_stat_template,
TP_PROTO(struct task_struct *tsk, u64 delay),
...
                __entry->pid    = tsk->pid;
...


Here is a patch, which allow us to get "foreign" events.
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e6dab5ffab59e910ec0e3355f4a6f29f7a7be474
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