linux-kernel - [PATCH 4/4] sched/fair: Improve NO_RUN_TO

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Message-ID: <20250613140514.2781138-5-vincent.guittot@linaro.org>
Date: Fri, 13 Jun 2025 16:05:14 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	linux-kernel@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 4/4] sched/fair: Improve NO_RUN_TO_PARITY

The slice protection of RUN_TO_PARITY should also be applied with a
minimal quantum of time for NO_RUN_TO_PARITY in order to ensure a minimum
runtime for each task with same slice duration but also to ensure
periodic switch between threads.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 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 d8345219dfd4..73bde511c53b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -921,15 +921,20 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
  * one in vlag, which isn't used until dequeue.
  * In case of run to parity, we use the shortest slice of the enqueued
  * entities.
+ * When run to parity is disable we give a minimum quantum to the
+ * running entity to ensure progress.
  */
 static inline void set_protect_slice(struct sched_entity *se)
 {
-	u64 min_slice;
+	u64 quantum;
 
-	min_slice = cfs_rq_min_slice(cfs_rq_of(se));
+	if (sched_feat(RUN_TO_PARITY))
+		quantum = cfs_rq_min_slice(cfs_rq_of(se));
+	else
+		quantum = min(se->slice, normalized_sysctl_sched_base_slice);
 
-	if (min_slice != se->slice)
-		se->vlag = min(se->deadline, se->vruntime + calc_delta_fair(min_slice, se));
+	if (quantum != se->slice)
+		se->vlag = min(se->deadline, se->vruntime + calc_delta_fair(quantum, se));
 	else
 		se->vlag = se->deadline;
 }
@@ -981,7 +986,7 @@ static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
 	if (curr && (!curr->on_rq || !entity_eligible(cfs_rq, curr)))
 		curr = NULL;
 
-	if (sched_feat(RUN_TO_PARITY) && curr && protect_slice(curr))
+	if (curr && protect_slice(curr))
 		return curr;
 
 	/* Pick the leftmost entity if it's eligible */
@@ -1215,11 +1220,8 @@ static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
 	cgroup_account_cputime(p, delta_exec);
 }
 
-static inline bool did_preempt_short(struct cfs_rq *cfs_rq, struct sched_entity *curr)
+static inline bool resched_next_quantum(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 {
-	if (!sched_feat(PREEMPT_SHORT))
-		return false;
-
 	if (protect_slice(curr))
 		return false;
 
@@ -1307,7 +1309,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	if (cfs_rq->nr_queued == 1)
 		return;
 
-	if (resched || did_preempt_short(cfs_rq, curr)) {
+	if (resched || resched_next_quantum(cfs_rq, curr)) {
 		resched_curr_lazy(rq);
 		clear_buddies(cfs_rq, curr);
 	}
-- 
2.43.0