The following tweaks help you tune performance with regards to CPUs in XenServer.
We discussed this in the VMware section and it applies to any hypervisor, including XenServer. Power management options enabled through the BIOS reduce the clock speed on the CPUs. Go into the BIOS and either disable power management or set it to the highest setting for maximum performance. Don't hinder the CPU's you invested all that money in.
You can pin VMs to CPUs, give VMs higher weighted priorities for CPU time and cap VMs usage on CPUs. Leave the default settings and let the XenServer hypervisor do the work.
There are some command line tools you can use to check the CPU usage on your ...