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!
On 12/11/2007, Feng Xian feng.xian@gmail.com 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.
Rui
On Mon, Nov 12, 2007 at 09:48:41AM +0000, Rui Tiago Matos wrote:
On 12/11/2007, Feng Xian feng.xian@gmail.com 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
On Mon, Nov 12, 2007 at 09:52:49AM -0500, Bill Rugolsky Jr. wrote:
With CPU hotplug, you don't even have to reboot.
One additional note: Since the Opteron boxes are NUMA, the memory topology (and any differences from the online CPU topology) may also affect your performance benchmark results.
-Bill
On Mon, 2007-11-12 at 10:00 -0500, Bill Rugolsky Jr. wrote:
On Mon, Nov 12, 2007 at 09:52:49AM -0500, Bill Rugolsky Jr. wrote:
With CPU hotplug, you don't even have to reboot.
One additional note: Since the Opteron boxes are NUMA, the memory topology (and any differences from the online CPU topology) may also affect your performance benchmark results.
-Bill
OT question: If he off-lines a certain CPU - doesn't he also disables all the HT links that belong to this CPU? (Along with their DRAM banks and I/O links?)
- Gilboa
kernel@lists.fedoraproject.org
-
Bill Rugolsky Jr. -
Feng Xian -
Gilboa Davara -
Rui Tiago Cação Matos