Find number of CPUs in linux kernel

Question

I want detect number of CPUs in linux kernel and write a sys_call that find it.

cpuinfo_x86 gives features of one CPU and cpu_detect fills it but how to find number of CPUs to detect?

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score 6 · Accepted Answer · answered Apr 03 '17 at 14:21

Using the MACRO NR_CPUS we can find the number of CPU. This Macro should not be used in early_init sequence Since mostly NR_CPUS will not be initialized as it is run time macro.

or you can use num_online_cpus() function to get the number of cpus online.

you can find more options in include/linux/cpumask.h header to find availability of CPUS in various kinds.

score 2 · Answer 2 · edited Jun 22 '22 at 08:01

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You can use nr_cpu_ids variable which is set by all architectures during kernel boot up and initialization.

edited Jun 22 '22 at 08:01

Glorfindel

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answered Apr 02 '17 at 18:37

0xAX

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score -2 · Answer 3 · answered Apr 02 '17 at 18:15

-2

Try:

$lscpu

This gives me information about CPUs, as well as architecture, etc...

answered Apr 02 '17 at 18:15

jedruniu

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The question is about finding information from **the kernel**, not from the *user space*. – Tsyvarev Apr 02 '17 at 18:25
In that case http://stackoverflow.com/questions/7315907/how-to-find-physical-and-logical-core-number-in-a-kernel-module – jedruniu Apr 02 '17 at 18:27
The referenced question is about a number of *current CPU*, not about of **total CPU** number. – Tsyvarev Apr 02 '17 at 18:39
in kernel mode not in user space – user3105001 Apr 02 '17 at 18:41

score -2 · Answer 4 · answered Apr 02 '17 at 19:38

-2

Personally, I cat /proc/cpuinfo to learn about the CPUs on a machine.

answered Apr 02 '17 at 19:38

rreck

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cat /proc/cpuinfo |grep processor |wc -l – rreck Oct 31 '17 at 13:25
yeah, i indeed missed the mark on this answer completely. – rreck Oct 31 '17 at 20:44

Find number of CPUs in linux kernel

4 Answers4