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

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Message-ID: <f3c045a6-2ed9-c948-04c9-325649b1dfe0@bytedance.com>
Date:   Wed, 6 Jul 2022 17:51:03 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Josh Don <joshdon@...gle.com>, Chen Yu <yu.c.chen@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/7] sched/fair: improve scan efficiency of SIS

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.
> 
> ...
>