linux-kernel - Re: [RFC PATCH v3 00/16] Core scheduling v3

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Date:   Thu, 10 Oct 2019 10:29:47 -0400
From:   Vineeth Remanan Pillai <vpillai@...italocean.com>
To:     Aaron Lu <aaron.lu@...ux.alibaba.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v3 00/16] Core scheduling v3

> I didn't see why we need do this.
>
> We only need to have the root level sched entities' vruntime become core
> wide since we will compare vruntime for them across hyperthreads. For
> sched entities on sub cfs_rqs, we never(at least, not now) compare their
> vruntime outside their cfs_rqs.
>
The reason we need to do this is because, new tasks that gets created will
have a vruntime based on the new min_vruntime and old tasks will have it
based on the old min_vruntime and it can cause starvation based on how
you set the min_vruntime. With this new patch, we normalize the whole
tree so that new tasks and old tasks compare with the same min_vruntime.

Thanks,
Vineeth