Messages in this thread Patch in this message | | | From | Dietmar Eggemann <> | Subject | [PATCH] sched/deadline: Reduce rq lock contention in dl_add_task_root_domain() | Date | Tue, 19 Jan 2021 09:35:42 +0100 |
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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 <qperret@google.com> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> ---
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
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