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

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Message-ID: <e1c4a7ed-822e-93cb-ff1d-6a0842db115f@linux.intel.com>
Date:   Tue, 6 Aug 2019 10:03:29 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Aaron Lu <aaron.lu@...ux.alibaba.com>
Cc:     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>,
        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

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.

Tim