Re: [Xen-devel] [RFC PATCH v1 00/16] xen: sched: implement core-scheduling

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Fri, Aug 24, 2018 at 5:36 PM Dario Faggioli <dfaggioli@xxxxxxxx> wrote:
>
> Hello,
>
> As anticipated here:
> https://lists.xenproject.org/archives/html/xen-devel/2018-08/msg02052.html
>
> Here's a preliminary version of my work, trying to implement
> core-scheduling in Xen.
>
> First of all, this deals with Credit1 only. I have patches for Credit2,
> and I've been working on having them ready by today, but I could not
> defeat the latest bugs. :-/
> I'll post them when back from vacation. Just let me anticipate, that
> doing something like this in Credit2, is a lot simpler than what you
> see here for Credit1.
>
> Even these patches that I'm posting are not perfect, and In fact there
> are some TODOs and XXXs --both in the changelogs and in the code.
>
> They give me a system that boots, where I can do basic stuff (like
> playing with dom0, creating guests, etc), and where the constraint of
> only scheduling vcpus from one domain at a time on pcpus that are part
> of the same core is, as far as I've seen, respected.
>
> There are still cases where the behavior is unideal, e.g., we could
> make a better use of some of the cores which are, some of the times,
> left idle.
>
> There are git branches here:
>  https://gitlab.com/dfaggioli/xen.git rel/sched/core-scheduling-RFCv1
>  https://github.com/fdario/xen.git rel/sched/core-scheduling-RFCv1
>
> Any comment is more than welcome.

Hi Dario,
thanks for the series, we are in the process of evaluating it in terms
of performance. Our test is to setup 2 VMs each being assigned enough
vCPUs to completely saturate all hyperthreads and then we fire up CPU
benchmarking inside the VMs to spin each vCPU 100% (using swet). The
idea is to force the scheduler to move vCPUs in-and-out constantly to
see how much performance hit there would be with core-scheduling vs
plain credit1 vs disabling hyperthreading. After running the test on a
handful of machines it looks like we get the best performance with
hyperthreading completely disabled, which is a bit unexpected. Have
you or anyone else encountered this?

Thanks,
Tamas

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