Re: Very high scheduling delay with plenty of idle CPUs

[Vincent Guittot]

On Fri, 8 Nov 2024 at 08:28, Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
>
> Hi scheduler folks,
>
> I'm running into some weird scheduling issues when testing non-sched
> changes on a Pixel 6 that's running close to 6.12-rc5. I'm not sure if
> this is an issue in earlier kernel versions or not.
>
> The async suspend/resume code calls async_schedule_dev_nocall() to
> queue up a bunch of work. These queued up work seem to be running in
> kworker threads.
>
> However, there have been many times where I see scheduling latency
> (runnable, but not running) of 4.5 ms or higher for a kworker thread
> when there are plenty of idle CPUs.

You are using EAS, aren't you ?
so the energy impact drive the cpu selection not cpu idleness

There is a proposal to change feec to also take into account such case
in addition to the energy impact
https://lore.kernel.org/lkml/64ed0fb8-12ea-4452-9ec2-7ad127b65529@xxxxxxx/T/

I still have to finalize v2

>
> Does async_schedule_dev_nocall() have some weird limitations on where
> they can be run? I know it has some NUMA related stuff, but the Pixel
> 6 doesn't have NUMA. This oddity unnecessarily increases
> suspend/resume latency as it adds up across kworker threads. So, I'd
> appreciate any insights on what might be happening?
>
> If you know how to use perfetto (it's really pretty simple, all you
> need to know is WASD and clicking), here's an example:
> https://ui.perfetto.dev/#!/?s=e20045736e7dfa1e897db6489710061d2495be92
>
> Thanks,
> Saravana