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Subject[PATCH v3 3/5] sched/deadline: reduce rq lock contention by eliminating locking of non-feasible target
Date
This patch adds check that prevents futile attempts to move dl tasks to
a CPU with active tasks of equal or earlier deadline. The same behavior as
commit 80e3d87b2c55 ("sched/rt: Reduce rq lock contention by eliminating
locking of non-feasible target") for rt class.

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v1 -> v2:
* add check in find_lock_later_rq()

kernel/sched/deadline.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 4303af2..e49b1e6 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1012,7 +1012,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
(p->nr_cpus_allowed > 1)) {
int target = find_later_rq(p);

- if (target != -1)
+ if (target != -1 &&
+ dl_time_before(p->dl.deadline,
+ cpu_rq(target)->dl.earliest_dl.curr))
cpu = target;
}
rcu_read_unlock();
@@ -1360,6 +1362,17 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)

later_rq = cpu_rq(cpu);

+ if (!dl_time_before(task->dl.deadline,
+ later_rq->dl.earliest_dl.curr)) {
+ /*
+ * Target rq has tasks of equal or earlier deadline,
+ * retrying does not release any lock and is unlikely
+ * to yield a different result.
+ */
+ later_rq = NULL;
+ break;
+ }
+
/* Retry if something changed. */
if (double_lock_balance(rq, later_rq)) {
if (unlikely(task_rq(task) != rq ||
--
1.9.1


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