Re: [PATCH v9] sched/fair: Filter false overloaded_group case for EAS

[Christian Loehle <christian.loehle@arm.com>]

On 2/11/26 01:48, Qais Yousef wrote:
> On 02/06/26 10:54, Vincent Guittot wrote:
>> With EAS, a group should be set overloaded if at least 1 CPU in the group
>> is overutilized but it can happen that a CPU is fully utilized by tasks
>> because of clamping the compute capacity of the CPU. In such case, the CPU
>> is not overutilized and as a result should not be set overloaded as well.
>>
>> group_overloaded being a higher priority than group_misfit, such group can
>> be selected as the busiest group instead of a group with a mistfit task
>> and prevents load_balance to select the CPU with the misfit task to pull
>> the latter on a fitting CPU.
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
>> Tested-by: Pierre Gondois <pierre.gondois@arm.com>
>> ---
>>
>> This patch was part of a larger patchset [1] but makes sense on its own and has
>> not changed since v2
>>
>> [1] https://lore.kernel.org/all/20251202181242.1536213-1-vincent.guittot@linaro.org/
> 
> I don't mind this. But I think with the original series misfit will be handled
> better with push lb, and if it is made to handle overloaded case (which my
> initial testing shows it is easily doable and I can't see clear bad impact
> yet), I think we can retire overutilized altogether.
> 

The EAS wakeup path (and therefore the push lb for that matter) is costly and workloads
are sensitive to it, it's trivial to see with hackbench. Overutilized prevents that.
Arguments about PELT inaccuracies during periods of unmet compute demand (and therefore
entirely bogus EAS computation results) aside, I don't see how we a push lb could retire
OU? If anything you're paying twice the price then for these scenarios?

> [snip]