Re: [RFC PATCH 3/7] sched/fair: Handle unthrottle path for task based throttle

[Aaron Lu <ziqianlu@bytedance.com>]

Hi Prateek,

On Fri, Mar 14, 2025 at 11:22:20PM +0530, K Prateek Nayak wrote:
... ... 
> but with per-task model, it is probably the amount of time that
> "throttled_limbo_list" has a task on it since they are runnable
> but are in-fact waiting for an unthrottle.

I tried this way of accounting and realized a problem. Assume a
hierarchy like this: /sys/fs/cgroup/1/1_1, quota configured at
/sys/fs/cgroup/1 level. When throttle happend and tasks of 1_1 get
throttled, the limbo list of /sys/fs/cgroup/1 will always be empty so
its "throttled_clock_self_time" is always 0...This doesn't match
throttled_clock_self_time's semantic. "throttled_time" is similar.

I suppose we can somehow fix this by introducing something like
h_nr_throttled, but I feel that's an overkill. So I'll probabaly just
keep the current accounting as is in the next version, feel free to let
me know if you have other thoughts.

Thanks.

> If a task enqueues itself on a throttled hierarchy and then blocks
> again before exiting to the userspace, it should not count in
> "throttled_clock_self_time" since the task was runnable the whole
> time despite the hierarchy being frozen.