CODEWITHSUNDEEP
clinuxlinux-kernellinux-device-driversmp
md.jamal
md.jamal

Reputation: 4567

nr_cpu_ids vs NR_CPUS in Linux Kernel

I am trying to understand how many processors are supported by Linux Kernel.

grep NR_CPUS /boot/config-`uname -r`

Will give me the maximum number of processors supported by kernel, which I can override using kernel command line parameter nr_cpus.

To find number of online cpus, i can use num_online_cpus() function

Then what is nr_cpu_ids?

#include <linux/kernel.h>
#include <linux/module.h>

MODULE_LICENSE("GPL");


static int __init test_hello_init(void)
{
    pr_info("%s: In init NR_CPUs=%d, nr_cpu_ids=%d\n", __func__, NR_CPUS, nr_cpu_ids);
    pr_info("Number of cpus available:%d\n", num_online_cpus());
    return -1;
}

static void __exit test_hello_exit(void)
{
    pr_info("%s: In exit\n", __func__);
}

module_init(test_hello_init);
module_exit(test_hello_exit);

[11548.627338] test_hello_init: In init NR_CPUs=8192, nr_cpu_ids=128
[11548.627340] Number of cpus available:6

What is the difference between NR_CPUs and ncr_cpu_ids. Are they not same?

Upvotes: 3

Views: 2083

Answers (1)

xman
xman

Reputation: 61

nr_cpu_ids is the total number of CPUs or processors in the machine while NR_CPUS is the total number of CPUs the Linux O/S can handle.

Upvotes: 5

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