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

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Date:   Tue, 6 Aug 2019 19:12:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Aaron Lu <aaron.lu@...ux.alibaba.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        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

On Tue, Aug 06, 2019 at 10:03:29AM -0700, Tim Chen wrote:
> On 8/5/19 8:24 PM, Aaron Lu wrote:
> 
> > I've been thinking if we should consider core wide tenent fairness?
> > 
> > Let's say there are 3 tasks on 2 threads' rq of the same core, 2 tasks
> > (e.g. A1, A2) belong to tenent A and the 3rd B1 belong to another tenent
> > B. Assume A1 and B1 are queued on the same thread and A2 on the other
> > thread, when we decide priority for A1 and B1, shall we also consider
> > A2's vruntime? i.e. shall we consider A1 and A2 as a whole since they
> > belong to the same tenent? I tend to think we should make fairness per
> > core per tenent, instead of per thread(cpu) per task(sched entity). What
> > do you guys think?
> > 
> > Implemention of the idea is a mess to me, as I feel I'm duplicating the
> > existing per cpu per sched_entity enqueue/update vruntime/dequeue logic
> > for the per core per tenent stuff.
> 
> I'm wondering if something simpler will work.  It is easier to maintain fairness
> between the CPU threads.  A simple scheme may be if the force idle deficit
> on a CPU thread exceeds a threshold compared to its sibling, we will
> bias in choosing the task on the suppressed CPU thread.  
> The fairness among the tenents per run queue is balanced out by cfq fairness,
> so things should be fair if we maintain fairness in CPU utilization between
> the two CPU threads.

IIRC pjt once did a simle 5ms flip flop between siblings.