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SubjectRe: [PATCH 1/3] sched/core: Fix the bug that task won't enqueue into core tree when update cookie
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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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