From: Cruz Zhao CruzZhao@linux.alibaba.com
mainline inclusion from mainline-v6.0-rc1 commit 91caa5ae242465c3ab9fd473e50170faa7e944f4 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5OOWG CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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 CruzZhao@linux.alibaba.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/1656403045-100840-2-git-send-email-CruzZhao@linux.... Conflicts: kernel/sched/core_sched.c [Feature 4feee7d12603d("sched/core: Forced idle accounting") is not applied.] Signed-off-by: Lin Shengwang linshengwang1@huawei.com Reviewed-by: lihua hucool.lihua@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.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 517f72b008f5..447e708e22d2 100644 --- a/kernel/sched/core_sched.c +++ b/kernel/sched/core_sched.c @@ -59,7 +59,6 @@ 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);
@@ -71,14 +70,16 @@ 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);
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);
/*