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Thu, 27 Feb 2025 00:58:46 -0800 (PST) From: Abel Wu To: Madadi Vineeth Reddy , Phil Auld , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Josh Don , Tianchen Ding Cc: Abel Wu , linux-kernel@vger.kernel.org (open list:SCHEDULER) Subject: [PATCH v2 1/2] sched/fair: Do not let idle entities preempt others Date: Thu, 27 Feb 2025 16:58:12 +0800 Message-Id: <20250227085815.18131-2-wuyun.abel@bytedance.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20250227085815.18131-1-wuyun.abel@bytedance.com> References: <20250227085815.18131-1-wuyun.abel@bytedance.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" A task with SCHED_IDLE policy doesn't preempt others by definition, and the semantics are intended to be preserved when extending to cgroups introduced in commit 304000390f88 ("sched: Cgroup SCHED_IDLE support"). But current implementation allows idle entities to preempt each other on wakeup, which seems not behave as expected especially after commit faa42d29419d ("sched/fair: Make SCHED_IDLE entity be preempted in st= rict hierarchy") so fix this by explicitly skip wakeup preemption for idle entities. Fixes: 304000390f88 ("sched: Cgroup SCHED_IDLE support") Signed-off-by: Abel Wu Reviewed-by: Vincent Guittot Reviewed-by: Josh Don Reviewed-by: Madadi Vineeth Reddy --- kernel/sched/fair.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d042e94a79c3..aaa9822e9562 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8795,8 +8795,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, = struct task_struct *p, int pse_is_idle =3D se_is_idle(pse); =20 /* - * Preempt an idle entity in favor of a non-idle entity (and don't preempt - * in the inverse case). + * Preempt an idle entity in favor of a non-idle entity. */ if (cse_is_idle && !pse_is_idle) { /* @@ -8807,7 +8806,10 @@ static void check_preempt_wakeup_fair(struct rq *rq,= struct task_struct *p, int goto preempt; } =20 - if (cse_is_idle !=3D pse_is_idle) + /* + * IDLE entities do not preempt others. + */ + if (unlikely(pse_is_idle)) return; =20 /* --=20 2.37.3