Re: [Xen-users] Release 0.8.9 of GPL PV drivers for Windows

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, May 07, 2008 at 12:06:41AM -0400, Todd Deshane wrote:
> On Tue, May 6, 2008 at 11:53 PM, jim burns <jim_burn@xxxxxxxxxxxxx> wrote:
> > On Tuesday May 06 2008 11:13:36 pm Todd Deshane wrote:
> >  > I think that your experience (allowing Xen to do the scheduling itself is
> >  > most efficient and only try to tweak the scheduling in very special cases
> >  > and/or you really know what you are doing) should be considered
> >  > conventional wisdom.
> >  >
> >  > Can you refresh me on the recommendations of the Xen developers that you
> >  > are referring to?
> >
> >  I was responding to Pasi's comment:
> >
> >
> >  On Tuesday May 06 2008 03:21:29 am Pasi Kärkkäinen wrote:
> >
> > > I think you should re-test with vcpu=1.
> >  >
> >

And more thing for the number of vcpu's for the HVM guest.. I think Windows
installs UNI or SMP HAL during the install time.. I don't know what kind of
effect there is if you run SMP HAL with only a single (v)CPU ?

> > > Configure dom0 for 1 vcpu and domU for 1 vcpu and pin the domains to have 
> > > a
> >  > dedicated core. This way you're not sharing any pcpu's between the 
> > domains.
> >  > I think this is the "recommended" setup from xen developers for getting
> >  > maximum performance.
> >  >
> >  > I think the performance will be worse when you have more vcpus in use 
> > than
> >  > your actual pcpu count..
> >
> >
> In our Running Xen book [1] chapter 12 "Managing Guest Resources" it says:
> 
> "If you are planning on having a substantial number of guests running, we
> recommend sticking with the default VCPUs. The only place that VCPU
> pinning may be advantageous is to restrict a CPU to run only for Domain0.
> Each guest relies on the services Domain0 offers ..."
> 
> It goes on to talk about especially heavy I/O etc. etc.
> 
> I bring this up since a lot of thought went into the details of the book. Not
> that we will always be right, but continuing to sharpen our knowledge and
> working through the details can only help future versions etc.
> 

Yep. What I meant was if dom0 can't get enough CPU time it will impact all
vm's.. so at least in some cases it will help to dedicate a pcpu for dom0.

-- Pasi

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