On Mon, Nov 12, 2007 at 09:48:41AM +0000, Rui Tiago Matos wrote:
> On 12/11/2007, Feng Xian <feng.xian@xxxxxxxxx> wrote:
> > Hi,
> >
> > 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.
See Documentation/cpu-hotplug.txt:
...
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.]
Regards,
Bill Rugolsky
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