From 91caa5ae242465c3ab9fd473e50170faa7e944f4 Mon Sep 17 00:00:00 2001 From: Cruz Zhao Date: Tue, 28 Jun 2022 15:57:23 +0800 Subject: [PATCH] sched/core: Fix the bug that task won't enqueue into core tree when update cookie In function sched_core_update_cookie(), a task will enqueue into the core tree only when it enqueued before, that is, if an uncookied task is cookied, it will not enqueue into the core tree until it enqueue again, which will result in unnecessary force idle. Here follows the scenario: CPU x and CPU y are a pair of SMT siblings. 1. Start task a running on CPU x without sleeping, and task b and task c running on CPU y without sleeping. 2. We create a cookie and share it to task a and task b, and then we create another cookie and share it to task c. 3. Simpling core_forceidle_sum of task a and b from /proc/PID/sched And we will find out that core_forceidle_sum of task a takes 30% time of the sampling period, which shouldn't happen as task a and b have the same cookie. Then we migrate task a to CPU x', migrate task b and c to CPU y', where CPU x' and CPU y' are a pair of SMT siblings, and sampling again, we will found out that core_forceidle_sum of task a and b are almost zero. To solve this problem, we enqueue the task into the core tree if it's on rq. Fixes: 6e33cad0af49("sched: Trivial core scheduling cookie management") Signed-off-by: Cruz Zhao Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/1656403045-100840-2-git-send-email-CruzZhao@linux.alibaba.com --- kernel/sched/core_sched.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c index 5103502da7ba..93878cb2a46d 100644 --- a/kernel/sched/core_sched.c +++ b/kernel/sched/core_sched.c @@ -56,7 +56,6 @@ static unsigned long sched_core_update_cookie(struct task_struct *p, unsigned long old_cookie; struct rq_flags rf; struct rq *rq; - bool enqueued; rq = task_rq_lock(p, &rf); @@ -68,14 +67,16 @@ static unsigned long sched_core_update_cookie(struct task_struct *p, */ SCHED_WARN_ON((p->core_cookie || cookie) && !sched_core_enabled(rq)); - enqueued = sched_core_enqueued(p); - if (enqueued) + if (sched_core_enqueued(p)) sched_core_dequeue(rq, p, DEQUEUE_SAVE); old_cookie = p->core_cookie; p->core_cookie = cookie; - if (enqueued) + /* + * Consider the cases: !prev_cookie and !cookie. + */ + if (cookie && task_on_rq_queued(p)) sched_core_enqueue(rq, p); /*