[tip: sched/urgent] sched/fair: Only set slice protection at pick time

[tip-bot2 for Peter Zijlstra]

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

Commit-ID:     bcd74b2ffdd0a2233adbf26b65c62fc69a809c8e
Gitweb:        https://git.kernel.org/tip/bcd74b2ffdd0a2233adbf26b65c62fc69a809c8e
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Fri, 23 Jan 2026 16:49:09 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 23 Feb 2026 11:19:18 +01:00

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().

Fixes: 63304558ba5d ("sched/eevdf: Curb wakeup-preemption")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Tested-by: Shubhang Kaushik <shubhang@xxxxxxxxxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260219080624.561421378%40infradead.org
---
 kernel/sched/fair.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 56dddd4..f2b46c3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5445,7 +5445,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 }
 
 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);
 
@@ -5460,7 +5460,8 @@ 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(cfs_rq, se);
+		if (first)
+			set_protect_slice(cfs_rq, se);
 	}
 
 	update_stats_curr_start(cfs_rq, se);
@@ -8978,13 +8979,13 @@ again:
 				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);
 	}
@@ -13598,7 +13599,7 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 	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);
 	}