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Date:   Sun, 22 Nov 2020 22:44:42 +1100
From:   Balbir Singh <bsingharora@gmail.com>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     Nishanth Aravamudan <naravamudan@digitalocean.com>,
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Subject: Re: [PATCH -tip 09/32] sched/fair: Snapshot the min_vruntime of CPUs
 on force idle
Message-ID: <20201122114442.GD110669@balbir-desktop>
References: <20201117232003.3580179-1-joel@joelfernandes.org>
 <20201117232003.3580179-10-joel@joelfernandes.org>
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On Tue, Nov 17, 2020 at 06:19:39PM -0500, Joel Fernandes (Google) wrote:
> During force-idle, we end up doing cross-cpu comparison of vruntimes
> during pick_next_task. If we simply compare (vruntime-min_vruntime)
> across CPUs, and if the CPUs only have 1 task each, we will always
> end up comparing 0 with 0 and pick just one of the tasks all the time.
> This starves the task that was not picked. To fix this, take a snapshot
> of the min_vruntime when entering force idle and use it for comparison.
> This min_vruntime snapshot will only be used for cross-CPU vruntime
> comparison, and nothing else.
> 
> This resolves several performance issues that were seen in ChromeOS
> audio usecase.
> 
> NOTE: Note, this patch will be improved in a later patch. It is just
>       kept here as the basis for the later patch and to make rebasing
>       easier. Further, it may make reverting the improvement easier in
>       case the improvement causes any regression.
>

This seems cumbersome, is there no way to track the min_vruntime via
rq->core->min_vruntime?

Balbir Singh.