Re: [PATCH] sched: Distinguish sched_wakeup event when wake up a task which did schedule out or not.

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

On 05/12/2014 03:47 PM, Peter Zijlstra wrote:
> On Sun, May 11, 2014 at 02:52:24PM -0400, Steven Rostedt wrote:
>> On Sun, 11 May 2014 18:35:31 +0200
>> Peter Zijlstra <peterz@infradead.org> wrote:
>> I believe you may be misunderstanding Dongsheng. It has nothing to do
>> with the wake condition. But the "success" is basically saying, "did I
>> move the task on to the run queue?". That's a relevant piece of
>> information that the wake up event isn't currently showing.
>>
>> Let me ask you this; with Donsheng's patch, will there ever be a
>> sched_switch event when the wakeup event sees 'false' and the
>> sched_switch event see the task with a state other than "R"? And if so,
>> how did the task doing the wakeup event, wake up that task?
> But that has nothing what so fucking ever to do with 'success'. Reusing
> that trace argument for something entirely different is just retarded.

Hi Peter,

we need to distinguish the true_wakeup and false_wakeup because
we want to know the timestamp when a task moved into runqueue.
Then we can calculate the latency time in perf sched latency command.

Without this patch, we will always get wakeup events with .success==true,
and we can not get the accurate time of task on run queue waiting for
cpu.

In original design of sched:sched_wakeup, actually was what I described
in commit message, .success==true means task go into run queue. And
perf-sched.c does only care events with this type:

         /* Note for later, it may be interesting to observe the failing 
cases */
         if (!success)
                 return 0;

And if scheduler raise an wakeup event with .success=true in 
ttwu_do_wakeup(),
perf sched latency will find the last state of this task is not out of 
run queue. Then
it will be confused and print a bug message for it.

# perf sched latency|tail
   bash:3498             |      0.785 ms |        1 | avg:    0.000 ms | 
max:    0.000 ms | max at:  0.000000 s
   bash:3600             |      0.522 ms |        1 | avg:    0.000 ms | 
max:    0.000 ms | max at:  0.000000 s
   bash:3570             |      0.295 ms |        1 | avg:    0.000 ms | 
max:    0.000 ms | max at:  0.000000 s
   bash:3581             |      0.288 ms |        1 | avg:    0.000 ms | 
max:    0.000 ms | max at:  0.000000 s
   bash:3594             |      0.286 ms |        1 | avg:    0.000 ms | 
max:    0.000 ms | max at:  0.000000 s
  -----------------------------------------------------------------------------------------
   TOTAL:                |   2768.420 ms |    17331 |
  ---------------------------------------------------
   INFO: 0.482% state machine bugs (82 out of 17008)