Messages in this thread Patch in this message | | | Date | Fri, 9 Jan 2015 04:33:43 -0800 | From | tip-bot for Luca Abeni <> | Subject | [tip:sched/urgent] sched/deadline: Fix migration of SCHED_DEADLINE tasks |
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Commit-ID: 6a503c3be937d275113b702e0421e5b0720abe8a Gitweb: http://git.kernel.org/tip/6a503c3be937d275113b702e0421e5b0720abe8a Author: Luca Abeni <luca.abeni@unitn.it> AuthorDate: Wed, 17 Dec 2014 11:50:31 +0100 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Fri, 9 Jan 2015 11:18:56 +0100
sched/deadline: Fix migration of SCHED_DEADLINE tasks
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> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Juri Lelli <juri.lelli@gmail.com> Cc: <stable@vger.kernel.org> Cc: Dario Faggioli <raistlin@linux.it> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1418813432-20797-2-git-send-email-luca.abeni@unitn.it Signed-off-by: Ingo Molnar <mingo@kernel.org> --- 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); }
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