Hi, I need to know the difference between making a cpu logically offline and physically offline. I have read that the following command $ echo 0 > /sys/device/system/cpu/<cpu number>/online makes a cpu logically offline. It frees the cpu from interrupts and migrates running processes. But then what does it mean to make a cpu physically offline ? I referred to following article : http://www.kernel.org/doc/Documentation/cpu-hotplug.txt Here is the relevant excerpt : Q: Does hot-add/hot-remove refer to physical add/remove of cpus? A: The usage of hot-add/remove may not be very consistently used in the code. CONFIG_HOTPLUG_CPU enables logical online/offline capability in the kernel. To support physical addition/removal, one would need some BIOS hooks and the platform should have something like an attention button in PCI hotplug. CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of CPUs. Please help! Thanks Vaibhav Jain