Messages in this thread Patch in this message | | | From | Luca Abeni <> | Subject | [PATCH 1/2] Fix migration of SCHED_DEADLINE tasks | Date | Wed, 17 Dec 2014 11:50:31 +0100 |
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According to global EDF, tasks should be migrated between runqueues without checking if their scheduling deadlines and runtimes are valid. However, SCHED_DEADLINE currently performs such a check: a migration happens doing deactivate_task(rq, next_task, 0); set_task_cpu(next_task, later_rq->cpu); activate_task(later_rq, next_task, 0); which ends up calling dequeue_task_dl(), setting the new CPU, and then calling enqueue_task_dl(). enqueue_task_dl() then calls enqueue_dl_entity(), which calls update_dl_entity(), which can modify scheduling deadline and runtime, breaking global EDF scheduling. As a result, some of the properties of global EDF are not respected: for example, a taskset {(30, 80), (40, 80), (120, 170)} scheduled on two cores can have unbounded response times for the third task even if 30/80+40/80+120/170 = 1.5809 < 2
This can be fixed by invoking update_dl_entity() only in case of wakeup, or if this is a new SCHED_DEADLINE task.
Signed-off-by: Luca Abeni <luca.abeni@unitn.it> --- kernel/sched/deadline.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index e5db8c6..55af498 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -826,10 +826,10 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se, * parameters of the task might need updating. Otherwise, * we want a replenishment of its runtime. */ - if (!dl_se->dl_new && flags & ENQUEUE_REPLENISH) - replenish_dl_entity(dl_se, pi_se); - else + if (dl_se->dl_new || flags & ENQUEUE_WAKEUP) update_dl_entity(dl_se, pi_se); + else if (flags & ENQUEUE_REPLENISH) + replenish_dl_entity(dl_se, pi_se); __enqueue_dl_entity(dl_se); } -- 1.9.1
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