[tip: sched/core] sched/fair: Prepare pick_next_task() for delayed dequeue

tip-bot2 for Peter Zijlstra
2024-08-18T06:23:12Z

The following commit has been merged into the sched/core branch of tip:

Commit-ID: f12e148892ede8d9ee82bcd3e469e6d01fc077ac
Gitweb: https://git.kernel.org/tip/f12e148892ede8d9ee82bcd3e469e6d01fc077ac
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 23 May 2024 11:26:25 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 17 Aug 2024 11:06:43 +02:00

sched/fair: Prepare pick_next_task() for delayed dequeue

Delayed dequeue's natural end is when it gets picked again. Ensure
pick_next_task() knows what to do with delayed tasks.

Note, this relies on the earlier patch that made pick_next_task()
state invariant -- it will restart the pick on dequeue, because
obviously the just dequeued task is no longer eligible.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105029.747330118@infradead.org
---
kernel/sched/fair.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9a84903..a4f1f79 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5473,6 +5473,8 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
se->prev_sum_exec_runtime = se->sum_exec_runtime;
}

+static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags);
+
/*
* Pick the next process, keeping these things in mind, in this order:
* 1) keep things fair between processes/task groups
@@ -5481,16 +5483,27 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
* 4) do not run the "skip" process, if something else is available
*/
static struct sched_entity *
-pick_next_entity(struct cfs_rq *cfs_rq)
+pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
{
/*
* Enabling NEXT_BUDDY will affect latency but not fairness.
*/
if (sched_feat(NEXT_BUDDY) &&
- cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next))
+ cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next)) {
+ /* ->next will never be delayed */
+ SCHED_WARN_ON(cfs_rq->next->sched_delayed);
return cfs_rq->next;
+ }
+
+ struct sched_entity *se = pick_eevdf(cfs_rq);
+ if (se->sched_delayed) {
+ dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
+ SCHED_WARN_ON(se->sched_delayed);
+ SCHED_WARN_ON(se->on_rq);

- return pick_eevdf(cfs_rq);
+ return NULL;
+ }
+ return se;
}

static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);
@@ -8507,7 +8520,9 @@ again:
if (unlikely(check_cfs_rq_runtime(cfs_rq)))
goto again;

- se = pick_next_entity(cfs_rq);
+ se = pick_next_entity(rq, cfs_rq);
+ if (!se)
+ goto again;
cfs_rq = group_cfs_rq(se);
} while (cfs_rq);