Re: [Xen-users] Xen Performance

[Adam Wead <awead@xxxxxxxxxxx>]

On Jun 2, 2009, at 1:59 AM, Luke S Crawford wrote:

> Adam Wead <awead@xxxxxxxxxxx> writes:
>
> > On Jun 1, 2009, at 8:43 PM, Luke S Crawford wrote:
> > > Also note, I've seen better worst-case performance by giving each
> > > VM fewer
> > > VCPUs, and the xen guys are not kidding about dedicating a core  
> > > to the
> > > Dom0.   setting cpus="1-7" in your xm config file (assuming an 8
> > > core box)
> > > and giving dom0 only 1 vcpu makes a world of difference on heavily
> > > loaded boxes.
> > This may be a dumb question, but is that any different from or the
> > same as setting "dom0-cpus 1" in the xend-config.sxp file?  Are you
> > specifying "cpus=1-7" in the guest's config or the Xen daemon's  
> > config?
> > thanks in advance for clearing up my confusion,
> setting cpus="1-7" in the guest config file is important, because  
> otherwise
> the guests will run on all cpus, including the dom0 cpus.
>
> I believe the dom0 vcp0 is pinned to cpu0, vcpu1 is pinned to  
> cpu1 .... so
> setting dom0-cpus 1  will pin the dom0 cpu 0 to 0.
>
> just setting dom0-cpus in xend-config.sxp without setting cpus= in  
> the domu
> configs doesn't help much, because the guests still trample over  
> the one
> cpu the dom0 has.
Thanks!

So it looks like you have to set both, if you want your Dom0 to be  
completely guest free.  The xend-config.sxp file specifies which cpu  
to use, and the guest config file keeps the guests away from using it  
and only all the others.
...adam

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