Vcpu allocation

in /etc/rc.local:

xm sched-credit -d 0 -w 60000

in /etc/xen/xend-config.sxp:

(dom0-cpus 1)

in /etc/xen/domain:

vcpus=1
cpus="2,3,4,5,6,7"

(in this case, I am reserving 0 for dom0, and 1 for the domain that runs my nfs server.)