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

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Date:   Tue, 6 Aug 2019 14:56:24 +0800
From:   Aubrey Li <aubrey.intel@...il.com>
To:     Aaron Lu <aaron.lu@...ux.alibaba.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.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 Tue, Aug 6, 2019 at 11:24 AM Aaron Lu <aaron.lu@...ux.alibaba.com> wrote:
>
> On Mon, Aug 05, 2019 at 08:55:28AM -0700, Tim Chen wrote:
> > On 8/2/19 8:37 AM, Julien Desfossez wrote:
> > > We tested both Aaron's and Tim's patches and here are our results.
> > >
> > > Test setup:
> > > - 2 1-thread sysbench, one running the cpu benchmark, the other one the
> > >   mem benchmark
> > > - both started at the same time
> > > - both are pinned on the same core (2 hardware threads)
> > > - 10 30-seconds runs
> > > - test script: https://paste.debian.net/plainh/834cf45c
> > > - only showing the CPU events/sec (higher is better)
> > > - tested 4 tag configurations:
> > >   - no tag
> > >   - sysbench mem untagged, sysbench cpu tagged
> > >   - sysbench mem tagged, sysbench cpu untagged
> > >   - both tagged with a different tag
> > > - "Alone" is the sysbench CPU running alone on the core, no tag
> > > - "nosmt" is both sysbench pinned on the same hardware thread, no tag
> > > - "Tim's full patchset + sched" is an experiment with Tim's patchset
> > >   combined with Aaron's "hack patch" to get rid of the remaining deep
> > >   idle cases
> > > - In all test cases, both tasks can run simultaneously (which was not
> > >   the case without those patches), but the standard deviation is a
> > >   pretty good indicator of the fairness/consistency.
> >
> > Thanks for testing the patches and giving such detailed data.
>
> Thanks Julien.
>
> > I came to realize that for my scheme, the accumulated deficit of forced idle could be wiped
> > out in one execution of a task on the forced idle cpu, with the update of the min_vruntime,
> > even if the execution time could be far less than the accumulated deficit.
> > That's probably one reason my scheme didn't achieve fairness.
>
> 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?
>

I also think a way to make fairness per cookie per core, is this what you
want to propose?

Thanks,
-Aubrey

> 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.