Re: Very high scheduling delay with plenty of idle CPUs

[Saravana Kannan]

On Fri, Nov 8, 2024 at 12:31 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Thu, Nov 07, 2024 at 11:28:07PM -0800, Saravana Kannan 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.
> >
>
> It's a bit unfortunate you don't have a known good kernel there. Anyway,
> one thing that recently came up is that DELAY_DEQUEUE can cause some
> delays, specifically it can inhibit wakeup migration.

I disabled DELAY_DEQUEUE and I'm still seeing preemptions or
scheduling latency (after wakeup) when there are plenty of CPUs even
within the same cluster/frequency domain.

Can we tell the scheduler to just spread out all the tasks during
suspend/resume? Doesn't make a lot of sense to try and save power
during a suspend/resume. It's almost always cheaper/better to do those
quickly.

-Saravana


-Saravana

>
> You can either test with that feature turned off, or apply something
> like the following patch:
>
>   https://lkml.kernel.org/r/20241106135346.GL24862@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx