Re: [RFC PATCH 4/5] sched/fair: Use EAS also when overutilized

[Vincent Guittot]

On Thu, 3 Oct 2024 at 11:52, Quentin Perret <qperret@xxxxxxxxxx> wrote:
>
> On Thursday 03 Oct 2024 at 10:57:55 (+0200), Vincent Guittot wrote:
> > The current pelt algorithm track actual cpu utilization and can go
> > above cpu capacity (but not above 1024) so a  task utilization can
> > become bigger than a little cpu capacity
>
> Right, the time invariance thing. So yes, I still think that a mix of
> co-scheduling and task migrations (which is likely common in the
> overcommitted state) will cause some CPUs to appear lightly utilized at
> least transiently, hence tricking feec() into thinking it can help when
> it really can't.
>
> > As replied to Lukasz, if you want to discard utilization of a trask
> > you need to check the previous cpu
>
> Please help me out here because I'm still not quite sure what we're
> talking about. Could you please expand a bit?

If you consider that utilization of a task is meaningless because of
CPU overcommitment then you need to check if the prev cpu of the
waking task is/was overcommitted or not the last time the task run in
addition to the overcommitment of the next cpu

>
> Thanks,
> Quentin