dl_add_task_root_domain() is called during sched domain rebuild:
rebuild_sched_domains_locked()
partition_and_rebuild_sched_domains()
rebuild_root_domains()
for all top_cpuset descendants:
update_tasks_root_domain()
for all tasks of cpuset:
dl_add_task_root_domain()
Change it so that only the task pi lock is taken to check if the task
has a SCHED_DEADLINE (DL) policy. In case that p is a DL task take the
rq lock as well to be able to safely de-reference root domain's DL
bandwidth structure.
Most of the tasks will have another policy (namely SCHED_NORMAL) and
can now bail without taking the rq lock.
One thing to note here: Even in case that there aren't any DL user
tasks, a slow frequency switching system with cpufreq gov schedutil has
a DL task (sugov) per frequency domain running which participates in DL
bandwidth management.
Reviewed-by: Quentin Perret <[email protected]>
Signed-off-by: Dietmar Eggemann <[email protected]>
---
The use case in which this makes a noticeable difference is Android's
'CPU pause' power management feature.
It uses CPU hotplug control to clear a CPU from active state to force
all threads which are not per-cpu kthreads away from this CPU.
Making DL bandwidth management faster during sched domain rebuild helps
to reduce the time to pause/un-pause a CPU.
kernel/sched/deadline.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 5421782fe897..c7b1a63a053b 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2409,9 +2409,13 @@ void dl_add_task_root_domain(struct task_struct *p)
struct rq *rq;
struct dl_bw *dl_b;
- rq = task_rq_lock(p, &rf);
- if (!dl_task(p))
- goto unlock;
+ raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
+ if (!dl_task(p)) {
+ raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
+ return;
+ }
+
+ rq = __task_rq_lock(p, &rf);
dl_b = &rq->rd->dl_bw;
raw_spin_lock(&dl_b->lock);
@@ -2420,7 +2424,6 @@ void dl_add_task_root_domain(struct task_struct *p)
raw_spin_unlock(&dl_b->lock);
-unlock:
task_rq_unlock(rq, p, &rf);
}
--
2.25.1
