Linux driver example to print the current running CPU - smp_processor_id()

When you have multiple processors present in the system, and want to find out on which the processor your driver code is running, use smp_processor_id().

Header file: #include <linux/smp.h>

Example:

	#include <linux/module.h>
	#include <linux/kernel.h>
	#include <linux/init.h>
	#include <linux/smp.h>
	#include <linux/sched.h>
	#include <linux/kthread.h>
	#include <linux/delay.h>
	MODULE_LICENSE("GPL");
	static struct task_struct *my_task = NULL;
	static int my_kthread(void *data) {
	char *str = (char *)data;
	pr_info("my kthread data: %s\n", str);
	pr_info("my kthread smp_processor_id %d\n", smp_processor_id());
	while(!kthread_should_stop()) {
	msleep(5000);
	pr_info("my kthread: living. smp_processor_id %d\n", smp_processor_id());
	pr_info("=========================================\n");
	}
	pr_info("my kthread: stop\n");
	return 0;
	}
	static int __init my_init(void)
	{
	pr_info("my init.\n");
	pr_info("smp_processor_id %d\n", smp_processor_id());
	my_task = kthread_run(my_kthread, "hello my kthread", "mykthread-%s", "test");
	pr_info("my init finish.\n");
	pr_info("=========================================\n");
	return 0;
	}
	static void __exit my_exit(void)
	{
	pr_info("my exit.\n");
	pr_info("smp_processor_id %d\n", smp_processor_id());
	if (my_task) {
	pr_info("stop kthread\n");
	kthread_stop(my_task);
	}
	pr_info("my exit finish.\n");
	pr_info("=========================================\n");
	}
	module_init(my_init);
	module_exit(my_exit);

view raw test_smp_processor_id.c hosted with ❤ by GitHub

Output:

You can see from the above screenshot, the init function of the driver was running on Processor 1 and Kernel thread was running on Processor 4