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

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Message-ID: <CANaguZBgv5N2Spv-Ldio5Umn6qU7dC0Px66sL9s11W7SK3f4Hg@mail.gmail.com>
Date:   Fri, 11 Oct 2019 08:10:30 -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

> Thanks for the clarification.
>
> Yes, this is the initialization issue I mentioned before when core
> scheduling is initially enabled. rq1's vruntime is bumped the first time
> update_core_cfs_rq_min_vruntime() is called and if there are already
> some tasks queued, new tasks queued on rq1 will be starved to some extent.
>
> Agree that this needs fix. But we shouldn't need do this afterwards.
>
> So do I understand correctly that patch1 is meant to solve the
> initialization issue?

I think we need this update logic even after initialization. I mean, core
runqueue's min_vruntime can get updated every time when the core
runqueue's min_vruntime changes with respect to the sibling's min_vruntime.
So, whenever this update happens, we would need to propagate the changes
down the tree right? Please let me know if I am visualizing it wrong.

Thanks,
Vineeth