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Re: [PATCH V2 2/2] sched/deadline: Throttle a constrained deadline task activated after the deadline

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On 13/02/2017 20:05, Daniel Bristot de Oliveira wrote:
> To avoid this problem, in the activation of a constrained deadline
> task after the deadline but before the next period, throttle the
> task and set the replenishing timer to the begin of the next period,
> unless it is boosted.

my only comment is that, by throttling on (dl < wakeuptime < period), we force the app to sync its activation time with the kernel, and the cbs doesn't self-sync anymore with the app own periodicity, which is what normally happens with dl=period. With dl=period, we loose the cbs self-sync and we force the app to sync with the kernel periodic timer only if we use explicitly yield(), but now this becomes also implicit just if we set dl<period.

> 	attr.sched_policy   = SCHED_DEADLINE;
> 	attr.sched_runtime  = 2 * 1000 * 1000;		/* 2 ms */
> 	attr.sched_deadline = 2 * 1000 * 1000;		/* 2 ms */
> 	attr.sched_period   = 2 * 1000 * 1000 * 1000;	/* 2 s */
...
> On my box, this reproducer uses almost 50% of the CPU time, which is
> obviously wrong for a task with 2/2000 reservation.

just a note here: in this example of runtime=deadline=2ms, shall we rely
on a utilization-based test, then we should assume the task is taking 100%.
More precise tests for EDF with deadline<period would properly count the
1998ms/2000ms free space, instead.

my2c,

	T.
-- 
Tommaso Cucinotta, Computer Engineering PhD
Associate Professor at the Real-Time Systems Laboratory (ReTiS)
Scuola Superiore Sant'Anna, Pisa, Italy
http://retis.sssup.it/people/tommaso

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[PATCH V2 0/2] sched/deadline: Fixes for constrained deadline tasks Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-13 20:10 +0100
  [PATCH V2 2/2] sched/deadline: Throttle a constrained deadline task activated after the deadline Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-13 20:10 +0100
    Re: [PATCH V2 2/2] sched/deadline: Throttle a constrained deadline  task activated after the deadline Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it> - 2017-02-14 18:00 +0100
      Re: [PATCH V2 2/2] sched/deadline: Throttle a constrained deadline  task activated after the deadline Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-14 18:40 +0100
    Re: [PATCH V2 2/2] sched/deadline: Throttle a constrained deadline  task activated after the deadline Steven Rostedt <rostedt@goodmis.org> - 2017-02-14 20:40 +0100
  [PATCH V2 1/2] sched/deadline: Replenishment timer should fire in the next period Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-13 20:10 +0100
  [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow "Steven Rostedt (VMware)" <rostedt@goodmis.org> - 2017-02-14 20:30 +0100
    Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow luca abeni <luca.abeni@santannapisa.it> - 2017-02-14 23:50 +0100
      Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Steven Rostedt <rostedt@goodmis.org> - 2017-02-15 01:20 +0100
        Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Luca Abeni <luca.abeni@santannapisa.it> - 2017-02-15 08:50 +0100
          Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Juri Lelli <juri.lelli@arm.com> - 2017-02-15 11:30 +0100
            Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Peter Zijlstra <peterz@infradead.org> - 2017-02-15 12:40 +0100
            Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Luca Abeni <luca.abeni@santannapisa.it> - 2017-02-15 13:40 +0100
              Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Juri Lelli <juri.lelli@arm.com> - 2017-02-15 14:00 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Luca Abeni <luca.abeni@santannapisa.it> - 2017-02-15 14:20 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Juri Lelli <juri.lelli@arm.com> - 2017-02-15 15:20 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-15 14:40 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-02-15 14:50 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Steven Rostedt <rostedt@goodmis.org> - 2017-02-15 15:10 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Juri Lelli <juri.lelli@arm.com> - 2017-02-15 15:20 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it> - 2017-02-16 17:40 +0100
                Re: [PATCH 3/2] sched/deadline: Use deadline instead of period when  calculating overflow Steven Rostedt <rostedt@goodmis.org> - 2017-02-16 17:50 +0100

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