I've noticed this section in Xen 3.4 News(
http://mail-index.netbsd.org/port-xen/2009/03/02/msg004800.html):

CPU offline/hotplug: Xen 3.4 can offline

physical CPUs on CPU-core granularity.
CPU hotplugging works on CPU granularity.
It's meant as an recover-action for the case
of machine-check errors. This feature
requires Dom0 support to utilize it.
This feature has been almost tested

on Intel-CPUs only.

Then I downloaded the stable version from xen.org and installed.
But since the document is not updated, I don't know the detail method to
offline a physical CPU.


Can anyone give me the hint? Thanks very much!

-- 
Yours Sincerely,
Ting Shen