On Mon, Nov 12, 2007 at 09:48:41AM +0000, Rui Tiago Matos wrote:
On 12/11/2007, Feng Xian <feng.xian(a)gmail.com> wrote:
> I am doing a scalable test on a 16-core machine (8 dual-core amd
> processors). So I need to vary the processors from 1 to 16. But I
> couldnt remove the cores from motherboard. Is there any way to achieve
> this by changing the max number of processors in the kernel? Thanks!
>From Documentation/kernel-parameters.txt in a linux source tree:
maxcpus= [SMP] Maximum number of processors that an SMP kernel
should make use of. maxcpus=n : n >= 0 limits the
kernel to using 'n' processors. n=0 is a special case,
it is equivalent to "nosmp", which also disables
the IO APIC.
Just add that parameter on your grub config or directly on the grub shell.
With CPU hotplug, you don't even have to reboot.
Command Line Switches
maxcpus=n Restrict boot time cpus to n. Say if you have 4 cpus, using
maxcpus=2 will only boot 2. You can choose to bring the
other cpus later online, read FAQ's for more info.
additional_cpus=n (*) Use this to limit hotpluggable cpus. This option sets
cpu_possible_map = cpu_present_map + additional_cpus
Q: How do i logically offline a CPU?
A: Do the following.
#echo 0 > /sys/devices/system/cpu/cpuX/online
[echo 1 into the same file to bring it back online.]