Re: [PATCH v4 0/7] sched/fair: improve scan efficiency of SIS

[Abel Wu]

Gentle ping

On 6/19/22 8:04 PM, Abel Wu Wrote:
> The wakeup fastpath (select_idle_sibling or SIS) plays an important role
> in maximizing the usage of cpu resources and can greatly affect overall
> performance of the system.
>
> The SIS tries to find an idle cpu inside that LLC to place the woken-up
> task. The cache hot cpus will be checked first, then other cpus of that
> LLC (domain scan) if the hot ones are not idle.
>
> The domain scan works well under light workload by simply traversing
> the cpus of the LLC due to lots of idle cpus can be available. But this
> doesn’t scale well once the LLC gets bigger and the load increases, so
> SIS_PROP was born to limit the scan cost. For now SIS_PROP just limits
> the number of cpus to be scanned, but the way of how it scans is not
> changed.
>
> This patchset introduces the SIS filter to help improving scan efficiency
> when scan depth is limited. The filter only contains the unoccupied cpus,
> and is updated during SMT level load balancing. It is expected that the
> more overloaded the system is, the less cpus will be scanned.
>
> ...