[RFC 2/8] Correctly track the active utilisation for migrating tasks

From: Luca Abeni
Date: Thu Jan 14 2016 - 10:37:15 EST

Fix active utilisation accounting on migration: when a task is migrated
from CPUi to CPUj, immediately subtract the task's utilisation from
CPUi and add it to CPUj. This mechanism is implemented by modifying the
pull and push functions.

Note: this is not fully correct from the theoretical point of view
(the utilisation should be removed from CPUi only at the 0 lag time),
but doing the right thing would be _MUCH_ more complex (leaving the
timer armed when the task is on a different CPU... Inactive timers should
be moved from per-task timers to per-runqueue lists of timers! Bah...)
kernel/sched/deadline.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e779cce..8d7ee79 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1541,7 +1541,9 @@ retry:

deactivate_task(rq, next_task, 0);
+ clear_running_bw(&next_task->dl, &rq->dl);
set_task_cpu(next_task, later_rq->cpu);
+ add_running_bw(&next_task->dl, &later_rq->dl);
activate_task(later_rq, next_task, 0);
ret = 1;

@@ -1629,7 +1631,9 @@ static void pull_dl_task(struct rq *this_rq)
resched = true;

deactivate_task(src_rq, p, 0);
+ clear_running_bw(&p->dl, &src_rq->dl);
set_task_cpu(p, this_cpu);
+ add_running_bw(&p->dl, &this_rq->dl);
activate_task(this_rq, p, 0);
dmin = p->dl.deadline;