How can you determine which process scheduler is being used?

Question

I.e. is it the O(1) scheduler, the CFS scheduler, or an older one?

Solution

You can call sched_getscheduler(process_pid) to determine the scheduling policy for a process.

If /sys/kernel/uids exists, you have CFS. Or you could try

[[ -n $(awk '$3 == "load_balance_fair" {print;}' < /proc/kallsyms) ]] && 
  echo CFS

I'm not sure how you could distinguish the O(1) scheduler from other obsolete schedulers. You could use the kernel version I suppose, but since distributions applied patches to their shipped kernels, this will be unreliable.

Comments

[Karlson]

Which OS are you asking about?

[Gilles 'SO- stop being evil']

I assume you're talking about Linux? I don't think there's any other unix variant with these scheduler names.

[daveb]

It's a linux variant: RHEL

[Mikel]

That's what I thought at first, but it looks like the return value from sched_getscheduler doesn't tell you which process scheduler is being used, just what scheduling policy is being used for the current process (essentially: normal/batch/realtime/low priority).

[Batfan]

Yes. That's why the second and following sentences of my answer are there!

[Jaime]

The sched_setscheduler allows a program to define parameters for the scheduler. It is not selecting which scheduler O(1) or CFS the linux is using. Nowadays, since kernel 2.6.23, the official kernel uses the CFS scheduler -- You may check man7.org/linux/man-pages/man2/sched_setscheduler.2.html