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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>
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>
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|---|---|---|
| .. | ||
| auto_group.c | ||
| auto_group.h | ||
| clock.c | ||
| completion.c | ||
| core.c | ||
| cpuacct.c | ||
| cpuacct.h | ||
| cpudeadline.c | ||
| cpudeadline.h | ||
| cpupri.c | ||
| cpupri.h | ||
| cputime.c | ||
| deadline.c | ||
| debug.c | ||
| fair.c | ||
| features.h | ||
| idle_task.c | ||
| idle.c | ||
| Makefile | ||
| proc.c | ||
| rt.c | ||
| sched.h | ||
| stats.c | ||
| stats.h | ||
| stop_task.c | ||
| wait.c | ||