Messages in this thread | | | Date | Sun, 3 Jul 2022 22:19:38 +0800 | Subject | Re: [PATCH 1/3] sched/core: Fix the bug that task won't enqueue into core tree when update cookie | From | cruzzhao <> |
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Ping... This bug really affects the performance, and is this bugfix correct?
在 2022/6/28 下午3:57, Cruz Zhao 写道: > 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> > --- > kernel/sched/core_sched.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c > index 38a2cec..ba2466c 100644 > --- a/kernel/sched/core_sched.c > +++ b/kernel/sched/core_sched.c > @@ -75,7 +75,7 @@ static unsigned long sched_core_update_cookie(struct task_struct *p, > old_cookie = p->core_cookie; > p->core_cookie = cookie; > > - if (enqueued) > + if (task_on_rq_queued(p)) > sched_core_enqueue(rq, p); > > /*
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