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

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Message-ID: <20140513100333.GW30445@twins.programming.kicks-ass.net>
Date:	Tue, 13 May 2014 12:03:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
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 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.

But that's completely and utterly unrelated to success.

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