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

[K Prateek Nayak]

Hello Aaron,

On 4/2/2025 2:55 PM, Aaron Lu wrote:
> 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.

I agree it might an overkill. We can discuss this more on v2.

--
Thanks and Regards,
Prateek

> 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.