linux-kernel - Re: perf,tools: Remove usage of trace_sched

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Date:	Tue, 13 May 2014 19:10:02 +0900
From:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...nel.org>, <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf,tools: Remove usage of trace_sched_wakeup(.success)

On 05/13/2014 07:03 PM, Peter Zijlstra wrote:
> On Tue, May 13, 2014 at 03:34:32PM +0900, Dongsheng Yang wrote:
>> On 05/13/2014 04:22 PM, Ingo Molnar wrote:
>>> * Peter Zijlstra <peterz@...radead.org> wrote:
>>>
>>>> trace_sched_wakeup(.success) is a dead argument and has been for ages,
>>> Always 0, or random value?
>> Hi Ingo,
>>
>> It is always 1 currently.
>>
>> Peter believe that .success is not useful and I pointed that perf sched
>> latency
>> is using it now. Then he post this patch to remove the usage here.
>>
>> Please go to the following link for more about this issue.
> It is _not_ usable. You're proposing to abuse the existing parameter. A
> wakeup doing an enqueue or not has nothing _WHAT_SO_EVER_ to do with
> success.
>
> Now what I think you wanted to do is make it easier to match
> trace_sched_switch() statements with trace_sched_wakeup() statements.
> And since you only get the trace_sched_switch() on dequeue, you want to
> know which trace_sched_wakeup() calls did an enqueue.

Ha, yes, indeed. In perf sched latency, we need to know the timestamp
when a task enqueue and then we can calculate the delay time.
So I want to take the use of success parameter in trace_sched_wakeup()
to indicate that *this* wakeup did an enqueue.

But now I think it is okey if you really mind adding more tracepoints in
scheduler. And I posted a patch after your patch in this thread to make
perf sched latency work well.
>
> But that's completely and utterly unrelated to success.

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