Re: [Xen-devel] credit1 scheduler question.

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, Feb 08, 2012 at 12:18:39PM +0000, George Dunlap wrote:
> On Tue, Feb 7, 2012 at 8:12 PM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > Hey George,
> >
> > I was wondering if you could explain in simple terms how the scheduler would
> > handle per-physical CPU when there are say 16 guests (each guest is using
> > one VCPU), 32 physical CPUs and dom0 is not restricted to any CPUs. Would
> > the scheduler per physical CPU schedule: guest, dom0, guest, dom0, and so
> > on; or would it be more random? (I assume that both guest and dom0 would do
> > a hypercall yield too).
> 
> The scheduling would be random.  As far as I know, none of the
> schedulers (sedf, credit1, or credit2) treat domain 0 differently from
> any other domain.  Even guests which are very busy end up blocking
> quite a bit, so the total runtime ends up being fairly random anyway.
> Also, the dom0 vcpus are not pinned unless you specify dom0_pin_vcpus
> on the xen command-line; so by default they will migrate freely around
> the various cores.
> 
> Does that answer your question?
> 

I don't know if it's relevant to this discussion but I tend to often
increase the credit scheduler weight of dom0 vcpus to guarantee smooth 
operation of dom0.

http://wiki.xen.org/wiki/Xen_Best_Practices

-- Pasi


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