CODEWITHSUNDEEP
linux-kernelreal-timesched-deadline
Ehsan
Ehsan

Reputation: 51

Is there a 100 us minimum for deadline/period in sched-deadline?

I am following Minimal main in sched-deadline page in https://www.kernel.org/doc/Documentation/scheduler/sched-deadline.txt. From the manual:

In addition, under the current implementation, all of the parameter values must be at least 1024 (i.e., just over one microsecond, which is the resolution of the implementation), and less than 2^63. If any of these checks fails, sched_setattr(2) fails with the error EINVAL.

However, when I enter any value less than 100*000 (ns) (e.g 99 *1000) in deadline/period, I get error:

sched_setattr: Invalid argument

Here is my code, changed from Minimal-main in sched-deadline webpage:

/* This creates an execution_time/99 us reservation */
attr.sched_policy = SCHED_DEADLINE;
attr.sched_runtime = execution_time + 1024 ;
attr.sched_period = attr.sched_deadline =99*1000  ;
ret = sched_setattr(0, &attr, flags);
printf("We have called sched_setattr, and ret value is:%d\n", ret);
if (ret < 0) {
    done = 0;
    perror("sched_setattr");
    exit(-1);
}

What am I missing here?

Upvotes: 1

Views: 197

Answers (1)

Ehsan
Ehsan

Reputation: 51

The root/kernel/sched/deadline.c says it:

Default limits for DL period; on the top end we guard against small util tasks still getting ridiculously long effective runtimes, on the bottom end we guard against timer DoS.

    static unsigned int sysctl_sched_dl_period_max = 1 << 22; /* ~4 seconds */

    static unsigned int sysctl_sched_dl_period_min = 100;     /* 100 us */

Upvotes: 2

Related Questions