--- /dev/null
+What: /sys/devices/system/xen_cpu/
+Date: May 2012
+Contact: Liu, Jinsong <jinsong.liu@intel.com>
+Description:
+ A collection of global/individual Xen physical cpu attributes
+
+ Individual physical cpu attributes are contained in
+ subdirectories named by the Xen's logical cpu number, e.g.:
+ /sys/devices/system/xen_cpu/xen_cpu#/
+
+
+What: /sys/devices/system/xen_cpu/xen_cpu#/online
+Date: May 2012
+Contact: Liu, Jinsong <jinsong.liu@intel.com>
+Description:
+ Interface to online/offline Xen physical cpus
+
+ When running under Xen platform, it provide user interface
+ to online/offline physical cpus, except cpu0 due to several
+ logic restrictions and assumptions.