Kernel preemption -- demo does not work

[Bernhard Walle <bernhard.walle@xxxxxx>]

Hello,

I'm experimenting about kernel preemption. If I understand it
correctly, a process executing a syscall could be preempted by another
process with a higher priority.

I have a simple kernel module with a 10 seconds loop in the
init_module() function. This function should be preemptible because
it's the insmod process in the init_module system call.

But another process with SCHED_FIFO (prio 99) isn't run until the init
function exits.

The code is

    int __init preempt_test_init(void)
    {
        unsigned long end;

        end = jiffies + HZ * 10; /* 10 seconds */

        pr_info("Preempt_count = %d\n", preempt_count());
        while (time_before(jiffies, end));
        pr_info("End\n");
    }

and of the process

    int main(int argc, char *argv[])
    {
        int                     err;
        struct sched_param      parm;
        int                     counter = 0;

        memset(&parm, 0, sizeof (struct sched_param));
        parm.sched_priority = 99;

        err = sched_setscheduler(getpid(), SCHED_FIFO, &parm);
        if (err < 0) {
            perror("Cannot change scheduler");
            return 1;
        }

        while (true) {
            printf("Scheduled, count = %d\n", counter++);
            sleep(1);
        }

        return 0;
    }

Thanks!


Regards,
  Bernhard

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