["Standard" CentOS 5.5 Xen Virtualization installation.]

I'm setting up a new box on AMD Opteron platform.

I'm doing some preliminary baselines (no domUs running) with an inline Watt/VA meter.

It appears to enable full power management Xen dom0 must have all cpus by not limiting in kernel statement nor in xendconfig.sxp. In previous installations I cut them back to 1 or 2.

The bonus of all cpus appears to be a 16% to 20% reduction in wattage/va consumption at idle. Pretty substantial when I consider that my electric utility rates have increased 75% (yep) in the past two years alone.

My question is to anyone with experience with this is will I be seeing a significant performance hit on domU performance in either paravirtualized or fully virtualized guests (or both)?