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

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Message-ID: <20160329131343.3b2bcf76@gandalf.local.home>
Date:	Tue, 29 Mar 2016 13:13:43 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.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 Tue, 29 Mar 2016 13:10:34 -0300
Daniel Bristot de Oliveira <bristot@...hat.com> wrote:

> 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?

Well, we shouldn't have two tracepoints back to back.

> 
> >> >  		__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

Why did it go to sleep? The above is still not very useful. What do you
mean "blocking on a system call"?

-- Steve