linux-kernel - [PATCH 1/4] sched/fair: Only set slice protection at pick time

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Message-ID: <20260130094607.945348633@infradead.org>
Date: Fri, 30 Jan 2026 10:34:40 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...nel.org
Cc: peterz@...radead.org,
 juri.lelli@...hat.com,
 vincent.guittot@...aro.org,
 dietmar.eggemann@....com,
 rostedt@...dmis.org,
 bsegall@...gle.com,
 mgorman@...e.de,
 vschneid@...hat.com,
 linux-kernel@...r.kernel.org,
 wangtao554@...wei.com,
 quzicheng@...wei.com,
 kprateek.nayak@....com,
 wuyun.abel@...edance.com,
 dsmythies@...us.net
Subject: [PATCH 1/4] sched/fair: Only set slice protection at pick time

We should not (re)set slice protection in the sched_change pattern
which calls put_prev_task() / set_next_task().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5420,7 +5420,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
 }
 
 static void
-set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
+set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, bool first)
 {
 	clear_buddies(cfs_rq, se);
 
@@ -5435,7 +5435,8 @@ set_next_entity(struct cfs_rq *cfs_rq, s
 		__dequeue_entity(cfs_rq, se);
 		update_load_avg(cfs_rq, se, UPDATE_TG);
 
-		set_protect_slice(cfs_rq, se);
+		if (first)
+			set_protect_slice(cfs_rq, se);
 	}
 
 	update_stats_curr_start(cfs_rq, se);
@@ -8958,13 +8959,13 @@ pick_next_task_fair(struct rq *rq, struc
 				pse = parent_entity(pse);
 			}
 			if (se_depth >= pse_depth) {
-				set_next_entity(cfs_rq_of(se), se);
+				set_next_entity(cfs_rq_of(se), se, true);
 				se = parent_entity(se);
 			}
 		}
 
 		put_prev_entity(cfs_rq, pse);
-		set_next_entity(cfs_rq, se);
+		set_next_entity(cfs_rq, se, true);
 
 		__set_next_task_fair(rq, p, true);
 	}
@@ -13578,7 +13579,7 @@ static void set_next_task_fair(struct rq
 	for_each_sched_entity(se) {
 		struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
-		set_next_entity(cfs_rq, se);
+		set_next_entity(cfs_rq, se, first);
 		/* ensure bandwidth has been allocated on our new cfs_rq */
 		account_cfs_rq_runtime(cfs_rq, 0);
 	}