Re: EEVDF regression still exists

[Sapkal, Swapnil]

Hello Peter,

On 4/30/2025 3:32 PM, Peter Zijlstra wrote:
> On Tue, Apr 29, 2025 at 04:38:17PM -0500, Cristian Prundeanu wrote:
>
> > [1] https://github.com/aws/repro-collection/blob/main/repros/repro-mysql-EEVDF-regression/results/20250428/README.md
>
> That 'perf sched stats diff' output is completely broken -- probably
> trying to diff two different schedstat versions isn't working.

Yeah. Will add a check to bail out the diff command if schedstat versions
are not identical.

> Anyway, looking at the two individual reports side by side:
>
>   - schedule() left the processor idle             -- is up
>
> vs.
>
>   - pull_task() count on cpu newly idle            -- is down
>   - load_balance() success count on cpu newly idle -- is down
>
> Which seem related and would suggest we look at newidle balance. One of
> the things we've seen before is that newidle was affected by the shorter
> slice of EEVDF. But it is also quite possible something changed in the
> load-balancer here.
>
> Also of note is that .15 seems to have a lower number of 'ttwu() was
> called to wake up on the local cpu' -- which I'm not quite sure how to
> rhyme with the previous observation. The newidle thing seems to suggest
> not enough migrations, while this would suggest too many migrations.
--
Thanks and Regards,
Swapnil