Hot-add vCPU is not automatically activated in some SLES 11 guests

Products

• VMware vSphere ESXi

Issue/Introduction

Hot-add vCPU is not automatically activated in some SLES 11 guest operating systems.

If you hot add extra vCPUs to the virtual machine while it is running, the additional vCPUs should appear in the .vmx file, the VIC, and in the guest operating system interface. With a Linux guest, the additional vCPUs are not automatically activated, so they do not appear in programs like top, for example, that only list active processors.

Environment

VMware ESX 4.0.x
VMware ESXi 4.0.x Installable
VMware ESXi 4.0.x Embedded

Resolution

A processor added using hot-add must be activated in the Linux guest before it can be used.

To automatically activate a processor when using hot-add, create a file /etc/udev/rules.d/99-vmware-cpuhotplug-udev.rules in your virtual machine with the following contents:

#
# VMware CPU HotPlug automatization
#
# Automatically bring on-line added processors.
#

ACTION=="add", SUBSYSTEM=="cpu", ATTR{online}="1"

If you already added a processor with hot-add, activate the processors by issuing (as root) the following command:

for a in /sys/devices/system/cpu/cpu*/online; do echo "1" > "$a"; done