linux-kernel - [PATCH v3 5/6] sched/fair: Fix entity's lag with run to parity

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Message-ID: <20250708165630.1948751-6-vincent.guittot@linaro.org>
Date: Tue,  8 Jul 2025 18:56:29 +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,
	dhaval@...nis.ca,
	linux-kernel@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v3 5/6] sched/fair: Fix entity's lag with run to parity

When an entity is enqueued without preempting current, we must ensure
that the slice protection is updated to take into account the slice
duration of the newly enqueued task so that its lag will not exceed
its slice (+ tick).

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 85238f2e026a..d815609526d5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -889,12 +889,12 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
  * When run to parity is disabled, we give a minimum quantum to the running
  * entity to ensure progress.
  */
-static inline void set_protect_slice(struct sched_entity *se)
+static inline void set_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	u64 quantum;
 
 	if (sched_feat(RUN_TO_PARITY))
-		quantum = cfs_rq_min_slice(cfs_rq_of(se));
+		quantum = cfs_rq_min_slice(cfs_rq);
 	else
 		quantum = normalized_sysctl_sched_base_slice;
 	quantum = min(quantum, se->slice);
@@ -905,6 +905,13 @@ static inline void set_protect_slice(struct sched_entity *se)
 		se->vprot = se->deadline;
 }
 
+static inline void update_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
+	u64 quantum = cfs_rq_min_slice(cfs_rq);
+
+	se->vprot = min_vruntime(se->vprot, se->vruntime + calc_delta_fair(quantum, se));
+}
+
 static inline bool protect_slice(struct sched_entity *se)
 {
 	return ((s64)(se->vprot - se->vruntime) > 0);
@@ -5468,7 +5475,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		__dequeue_entity(cfs_rq, se);
 		update_load_avg(cfs_rq, se, UPDATE_TG);
 
-		set_protect_slice(se);
+		set_protect_slice(cfs_rq, se);
 	}
 
 	update_stats_curr_start(cfs_rq, se);
@@ -8730,6 +8737,9 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
 	if (__pick_eevdf(cfs_rq, !do_preempt_short) == pse)
 		goto preempt;
 
+	if (sched_feat(RUN_TO_PARITY) && do_preempt_short)
+		update_protect_slice(cfs_rq, se);
+
 	return;
 
 preempt:
-- 
2.43.0