On Wed, Aug 17, 2011 at 9:14 AM, Vaibhav Jain <vjoss197@gmail.com> wrote:
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
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Hi Vaibhav! I think physical CPU hot-plug is a capability to plug in and out processing device (CPU) on running machine. Logical CPU hot-plug is a capability to add on and remove out already available processing units (CPU s or cores) under SMP domain of OS. P.S. Sorry for my weak English.