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

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Date:   Thu, 15 Aug 2019 18:09:28 +0200
From:   Dario Faggioli <dfaggioli@...e.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:     Aaron Lu <aaron.lu@...ux.alibaba.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 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. :-)

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/
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