Xen - Make one guest OS have 2 cpus?

Question

I have inherited a Xen setup. The dom0 and domU's are all linux. dom0 has 8 cores (or CPUs, I'm not sure). We want to run more stuff on one domU. I want to make it a multicore CPU, ie so that the domU will see 2 cores.

How do I do this in xen?

I don't care about forcing it to run on 2 specific CPUs (if that's an acceptable solution, that's fine). We're using a generic domU kernel (from somewhere). I don't know if this kernel can support multicore cpus (or if that's even an issue), it's relatively recent, 2.6.26.

Answer 1

I believe you just add vcpus=2 to the guest's config file.

Answer 2

You need to add/modify the vcpus line in the guest's config, however you should be aware that some of the more recent versions of Xen manage the configuration via a backend buried somewhere in /var so you will require more than just a restart of the Guest for it to pick up the configuration changes. It may work fine with a simple restart of the xend service or a reboot. If that doesn't work, an xm destroy then xm create of the Guest should suffice.

(Usual caveat, back up your configs before something permanent like an xm destroy)