From eb24c281ee879fe6aff1f9cf26ee617ba501c6de Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Wed, 21 Jan 2026 17:33:17 +0100 Subject: [PATCH] sched/fair: Fix pelt clock sync when entering idle [ Upstream commit 98c88dc8a1ace642d9021b103b28cba7b51e3abc ] Samuel and Alex reported regressions of the util_avg of RT rq with commit 17e3e88ed0b6 ("sched/fair: Fix pelt lost idle time detection"). It happens that fair is updating and syncing the pelt clock with task one when pick_next_task_fair() fails to pick a task but before the prev scheduling class got a chance to update its pelt signals. Move update_idle_rq_clock_pelt() in set_next_task_idle() which is called after prev class has been called. Fixes: 17e3e88ed0b6 ("sched/fair: Fix pelt lost idle time detection") Closes: https://lore.kernel.org/all/CAG2KctpO6VKS6GN4QWDji0t92_gNBJ7HjjXrE+6H+RwRXt=iLg@mail.gmail.com/ Closes: https://lore.kernel.org/all/8cf19bf0e0054dcfed70e9935029201694f1bb5a.camel@mediatek.com/ Reported-by: Samuel Wu Reported-by: Alex Hoh Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Tested-by: Samuel Wu Tested-by: Alex Hoh Link: https://patch.msgid.link/20260121163317.505635-1-vincent.guittot@linaro.org Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 6 ------ kernel/sched/idle.c | 6 ++++++ 2 files changed, 6 insertions(+), 6 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1436d6bb86ec..6efb1dfcd943 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9033,12 +9033,6 @@ idle: goto again; } - /* - * rq is about to be idle, check if we need to update the - * lost_idle_time of clock_pelt - */ - update_idle_rq_clock_pelt(rq); - return NULL; } diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 53bb9193c537..624ef809f671 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -462,6 +462,12 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir scx_update_idle(rq, true, true); schedstat_inc(rq->sched_goidle); next->se.exec_start = rq_clock_task(rq); + + /* + * rq is about to be idle, check if we need to update the + * lost_idle_time of clock_pelt + */ + update_idle_rq_clock_pelt(rq); } struct task_struct *pick_task_idle(struct rq *rq)