[PATCH 4/6 v3] sched/eevdf: Cancel slice protection if short slice task is eligible

[Vincent Guittot]

If a short slice task will not be the next to be picked but is eligible,
we cancel the slice protection to speedup the time when the short slice
task will be the next to run.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
---
 kernel/sched/fair.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 854f3a9f1d80..719aa53851e4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9816,18 +9816,13 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
 	cse_is_idle = se_is_idle(se);
 	pse_is_idle = se_is_idle(pse);
 
+	nse = se;
 	/*
 	 * Preempt an idle entity in favor of a non-idle entity (and don't preempt
 	 * in the inverse case).
 	 */
-	if (cse_is_idle && !pse_is_idle) {
-		/*
-		 * When non-idle entity preempt an idle entity,
-		 * don't give idle entity slice protection.
-		 */
-		preempt_action = PREEMPT_WAKEUP_SHORT;
+	if (cse_is_idle && !pse_is_idle)
 		goto preempt;
-	}
 
 	if (cse_is_idle != pse_is_idle)
 		return;
@@ -9896,16 +9891,23 @@ static void wakeup_preempt_fair(struct rq *rq, struct task_struct *p, int wake_f
 	if (!nse && cfs_rq->nr_queued)
 		goto pick;
 
+	/*
+	 * If @p is eligible but not the next task to run then cancel protection
+	 * to prevent large scheduling latency
+	 */
+	if (preempt_action == PREEMPT_WAKEUP_SHORT && entity_eligible(cfs_rq, pse))
+		goto preempt;
+
 	if (sched_feat(RUN_TO_PARITY))
 		update_protect_slice(cfs_rq, se);
 
 	return;
 
 preempt:
-	if (preempt_action == PREEMPT_WAKEUP_SHORT) {
-		cancel_protect_slice(se);
+	cancel_protect_slice(se);
+
+	if (preempt_action == PREEMPT_WAKEUP_SHORT && nse == pse)
 		set_next_buddy(&p->se);
-	}
 
 	resched_curr_lazy(rq);
 }
-- 
2.43.0