linux-kernel - Re: [PATCH V2 3/3] sched/deadline: Tracepoints for deadline scheduler

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Date:	Tue, 29 Mar 2016 13:10:34 -0300
From:	Daniel Bristot de Oliveira <bristot@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Juri Lelli <juri.lelli@....com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH V2 3/3] sched/deadline: Tracepoints for deadline scheduler



On 03/29/2016 12:16 PM, Peter Zijlstra wrote:
>> +		trace_sched_deadline_yield(&rq->curr->dl);

ouch, it should be trace_sched_deadline_yield(dl_se). It works
as is, but it is really very sad, my bad, sorry.

>> >  		dl_se->dl_throttled = 1;
>> > +		trace_sched_deadline_throttle(dl_se);
> This is just really very sad.

Am I missing any other really very sad thing here?

>> >  		__dequeue_task_dl(rq, curr, 0);
>> >  		if (unlikely(dl_se->dl_boosted || !start_dl_timer(curr)))
>> >  			enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);
>> > @@ -910,6 +917,7 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
>> >  static void dequeue_dl_entity(struct sched_dl_entity *dl_se)
>> >  {
>> >  	__dequeue_dl_entity(dl_se);
>> > +	trace_sched_deadline_block(dl_se);
>> >  }
> And that's just not going to happen.

It will, if a task goes to sleep during the activation,
e.g., when blocking on a system call. For example:

          <idle>-0     [007] d..3 78377.688969: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=b next_pid=18973 next_prio=-1
               b-18973 [007] d..3 78377.688979: sched_deadline_block: now=78377.688976271 deadline=78377.718945137 remaining_runtime=9968866
               b-18973 [007] d..3 78377.688981: sched_switch: prev_comm=b prev_pid=18973 prev_prio=-1 prev_state=S ==> next_comm=swapper/7 next_pid=0 next_prio=120