Messages in this thread | | | Subject | Re: [PATCH V2 2/2] sched/deadline: Throttle a constrained deadline task activated after the deadline | From | Tommaso Cucinotta <> | Date | Tue, 14 Feb 2017 16:54:13 +0100 |
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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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