Programmatically disable CPU core

user_2856041 0
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It is known the way to disable logical CPUs in Linux, basically with echo 0 > /sys/devices/system/cpu/cpu<number>/online. This way, you are only telling to the OS to ignore that given (<number>) CPU.

My question goes further, is it possible not only to ignore it but to turn it off physically programmatically? I want that CPU to not receive any power, in order to make its energy consumption zero.

I know that it is possible disable cores from the BIOS (not always), but I want to know whether is possible to do it within a certain program or not.

hardware-programming hardware multicore processor linux
6 Answers

In Windows 10 it became possible with new power management commands CPMINCORES CPMAXCORES.

Powercfg -setacvalueindex scheme_current sub_processor CPMAXCORES 50
Powercfg -setacvalueindex scheme_current sub_processor CPMINCORES 25
Powercfg -setactive scheme_current

Here 50% of cores are assigned for desired deep sleep, and 25% are forbidden to be parked. Very good in numeric simulations requiring increased clock rate (15% boost on Intel)

You can not choose which cores to park, but Windows 10 kernel checks Intel's Comet Lake and newer "prefered" (more power efficient) cores, and starts parking those not preferred. It is not a strict parking, so at high load the kernel can use these cores with very low load.

just in case if you are looking for alternatives

user_100733340
user_23878350

I know this is an old question but one way to disable the CPU is via grub config.

If you add to end of GRUB_CMDLINE_LINUX in /etc/default/grub (assuming you are using a standard Linux dist, if you are using an appliance the location of the grub config may be different), e.g.:

GRUB_CMDLINE_LINUX=".......Current config here **maxcpus**=2"

Then remake you grub config by running grub2-mkconfig -o /boot/grub2/grub.cfg (or grub-mkconfig -o /boot/grub2/grub.cfg depending on your installation). Some distros may require nr_cpus instead of maxcpus.

Just some extra info:

  • If you are running a server with Multiple physical CPU then disabling one CPU may will most likely disable the memory set that is linked to that CPU, therefore it may have an effect on the performance of the server

  • Disabling the CPU this way, will not effect your type 1 hypervisor from accessing the CPU (this is based on xen hypervisor, I believe it will apply to vmware as well, if anyone can provide confirmation would be great). Depending on virtualbox setup, it may restrict the amount of CPU you can allocate to VM's unless you are running para-virtualization.

  • I am unsure however if you will have any power savings, most servers and even desktops these days, already control the power well, putting to sleep any device not needed for the current load. My concern would be by reducing the number of CPU (cores) then you will just be moving the load to the remaining CPU and due to the need to schedule the processors time, and potentially having instructions queued, and the effect of having a smaller number of cores available for interrupts (eg: network traffic), it may have a negative effect on power consumption.

user_83146380
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