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

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Date:   Fri, 16 Aug 2019 10:33:09 +0800
From:   Aaron Lu <aaron.lu@...ux.alibaba.com>
To:     Dario Faggioli <dfaggioli@...e.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.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>,
        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 Thu, Aug 15, 2019 at 06:09:28PM +0200, Dario Faggioli wrote:
> On Wed, 2019-08-07 at 10:10 -0700, Tim Chen wrote:
> > On 8/7/19 1:58 AM, Dario Faggioli wrote:
> > 
> > > Since I see that, in this thread, there are various patches being
> > > proposed and discussed... should I rerun my benchmarks with them
> > > applied? If yes, which ones? And is there, by any chance, one (or
> > > maybe
> > > more than one) updated git branch(es)?
> > > 
> > Hi Dario,
> > 
> Hi Tim!
> 
> > Having an extra set of eyes are certainly welcomed.
> > I'll give my 2 cents on the issues with v3.
> > 
> Ok, and thanks a lot for this.
> 
> > 1) Unfairness between the sibling threads
> > -----------------------------------------
> > One sibling thread could be suppressing and force idling
> > the sibling thread over proportionally.  Resulting in
> > the force idled CPU not getting run and stall tasks on
> > suppressed CPU.
> > 
> > 
> > [...]
> >
> > 2) Not rescheduling forced idled CPU
> > ------------------------------------
> > The forced idled CPU does not get a chance to re-schedule
> > itself, and will stall for a long time even though it
> > has eligible tasks to run.
> > 
> > [...]
> > 
> > 3) Load balancing between CPU cores
> > -----------------------------------
> > Say if one CPU core's sibling threads get forced idled
> > a lot as it has mostly incompatible tasks between the siblings,
> > moving the incompatible load to other cores and pulling
> > compatible load to the core could help CPU utilization.
> > 
> > So just considering the load of a task is not enough during
> > load balancing, task compatibility also needs to be considered.
> > Peter has put in mechanisms to balance compatible tasks between
> > CPU thread siblings, but not across cores.
> > 
> > [...]
> >
> Ok. Yes, as said, I've been trying to follow the thread, but thanks a
> lot again for this summary.
> 
> As said, I'm about to have numbers for the repo/branch I mentioned.
> 
> I was considering whether to also re-run the benchmarking campaign with
> some of the patches that floated around within this thread. Now, thanks
> to your summary, I have an even clearer picture about which patch does
> what, and that is indeed very useful.
> 
> I'll see about putting something together. I'm thinking of picking:
> 
> https://lore.kernel.org/lkml/b7a83fcb-5c34-9794-5688-55c52697fd84@linux.intel.com/
> https://lore.kernel.org/lkml/20190725143344.GD992@aaronlu/
> 
> And maybe even (part of):
> https://lore.kernel.org/lkml/20190810141556.GA73644@aaronlu/#t
> 
> If anyone has ideas or suggestions about whether or not this choice
> makes sense, feel free to share. :-)

Makes sense to me.
patch3 in the last link is slightly better than the one in the 2nd link,
so just use that instead.

Thanks,
Aaron

> Also, I only have another week before leaving, so let's see what I
> manage to actually run, and then share here, by then.
> 
> Thanks and Regards
> -- 
> Dario Faggioli, Ph.D
> http://about.me/dario.faggioli
> Virtualization Software Engineer
> SUSE Labs, SUSE https://www.suse.com/
> -------------------------------------------------------------------
> <<This happens because _I_ choose it to happen!>> (Raistlin Majere)
>