CODEWITHSUNDEEP
multithreadinglinux-kernelcpu
K_K
K_K

Reputation: 798

Not able to bind kernel threads to CPU

I have written this code to bind 2 kernel threads to different CPUs :

#include<linux/kthread.h>
#include<linux/sched.h>
#include<linux/delay.h>
#include<linux/slab.h>

struct task_struct *task1;
struct task_struct *task2;
int cpu, data;

int thread_function_one(void *data)
{
    int ret = 10;
    printk(KERN_INFO "IN THREAD FUNCTION 1 \n");

    while(!kthread_should_stop()){
       cpu = get_cpu();
       put_cpu();
       printk("t1 cpu = %d\n",cpu);
       msleep(5000);
    }
    printk(KERN_INFO "EXIT from thread function 1\n");
    return ret;
}

int thread_function_two(void *data)
{
    int ret = 10;
    printk(KERN_INFO "IN THREAD FUNCTION 2 \n");

    while(!kthread_should_stop()){
        cpu = get_cpu();
        put_cpu();
        printk("t2 cpu = %d\n",cpu);
        msleep(6000);
    }
    printk(KERN_INFO "EXIT from thread function 2\n");
    return ret;
}

static int kernel_init(void)
{
   printk(KERN_INFO "module_init\n");

   cpu = get_cpu();
   put_cpu();
   printk("main thread cpu = %d \n",cpu);

   task1 = kthread_create(&thread_function_one,(void *)&data,"one");
   kthread_bind(task1, cpu);
   wake_up_process(task1);

   cpu = 5;
   task2 = kthread_create(&thread_function_two,(void *)&data,"two");
   kthread_bind(task2, cpu);
   wake_up_process(task2);

   return 0;
}

static void kernel_exit(void)
{
   kthread_stop(task1);
   kthread_stop(task2);
   printk(KERN_INFO "module_exit\n");
}

module_init(kernel_init);
module_exit(kernel_exit);
MODULE_AUTHOR("K_K");
MODULE_LICENSE("GPL");

But when I print the cpu id in thread_function_one and thread_function_two both print the same CPU as that of main thread.

Am I doing smthing wrong ?

Output of this prog :

kernel: [  956.816510] module_init
kernel: [  956.816515] main thread cpu = 8 
kernel: [  956.816743] IN THREAD FUNCTION 1 
kernel: [  956.816748] t1 cpu = 8
kernel: [  956.817057] IN THREAD FUNCTION 2 
kernel: [  956.817062] t2 cpu = 8
kernel: [  961.815160] t1 cpu = 8
kernel: [  962.814649] t2 cpu = 8
kernel: [  966.816760] t1 cpu = 8
kernel: [  968.815711] t2 cpu = 8
kernel: [  971.818307] EXIT from thread function 1
kernel: [  974.816813] EXIT from thread function 2
kernel: [  974.816872] module_exit

Upvotes: 8

Views: 2843

Answers (1)

K_K
K_K

Reputation: 798

The module works fine if the "int cpu" variable is not global. The thread one modifies this global and thread two binds itself to the same CPU. This is the race condition between main thread, thread one and thread two.

Upvotes: 5

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