回复: 回复: [PATCH v2] sched/eevdf: Force propagating min_slice of cfs_rq when a task changing slice

[解 咏梅]

Let analyze it case by case:P

say cgroup A has 3 tasks: task A, task B, task C

1) assign taskA's slice to 0.1 ms, task B, tack C, task C all have the default slice (0.75ms)

2) task A is picked by __schedule as next task, because task A is still on rq, 
so the cfs_rq hierarchical doesn't have to change cfs_rq's min_slice, it will report it to the root cgroup

3)  task A is preempted by other task, it's still runnable. it will be requeued cgroup A's cfs_rq. similar as case 2

4) task A is preempted since it's blocked, task A's se will be retained in cgroup A's cfs_rq until it reach 0-lag state.
4.1 before 0-lag, I guess it's similar as case 2
     the logic is based on cfs_rq's avg_runtime, it supposed task A won't be pick as next task before it reach 0-lag state.
     If my understanding is wrong, pls correct me. Thanks.
4.2 After it reached 0-lag state, If it's picked by pick_task_fair, it will be removed from cgroup A cfs_rq ultimately.
     pick_next_entity->dequeue_entities(DEQUEUE_SLEEP | DEQUEUE_DELAYED)->__dequeue_entity (taskA)
    so, cgroup A's cfs_rq min_slice will be re-calculated. So the cfs_rq hierarchical  will modify their own min_slice bottom up.
4.3 After it reached 0-lag state, it will waked up. Because, the current __schedule() split the path for block/sleep from migration path. only migration path will call deactivate. so p->on_rq is still 1, ttwu_runnable will work for it to just call requeue_delayed_entity. similar as case 2

I think only case 1 has such problem.

Regards,
Yongmei.

________________________________________
发件人: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>
发送时间: 2024年11月14日 10:45
收件人: 解 咏梅 <xieym_ict@xxxxxxxxxxx>
抄送: Ingo Molnar <mingo@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Juri Lelli <juri.lelli@xxxxxxxxxx>; Vincent Guittot <vincent.guittot@xxxxxxxxxx>; Dietmar Eggemann <dietmar.eggemann@xxxxxxx>; Steven Rostedt <rostedt@xxxxxxxxxxx>; Ben Segall <bsegall@xxxxxxxxxx>; Mel Gorman <mgorman@xxxxxxx>; Valentin Schneider <vschneid@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>
主题: Re: 回复: [PATCH v2] sched/eevdf: Force propagating min_slice of cfs_rq when a task changing slice
 
On 2024/11/13 19:50, 解 咏梅 wrote:
> Similar problem as commit d2929762 & 8dafa9d0, but this time heap integrity is corrupted by min_slice attr.
> commit eab03c23c fixed it by explicitly calling __dequeue_entity and __enqueue_entity in reweight_entity.
>
> But, it's rare case, it only happens when adjust task's select by setting up scheduler attribute.
>

It's not rare. Since it's in enqueue/dequeue common path, wakeup/sleep may also
trigger this issue.

>
> Regards,
> Yongmei.