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

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Which OS are you asking about? –  Karlson Apr 17 '12 at 14:42
I assume you're talking about Linux? I don't think there's any other unix variant with these scheduler names. –  Gilles Apr 17 '12 at 23:39
It's a linux variant: RHEL –  daveb Apr 18 '12 at 10:55
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2 Answers

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.

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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). –  Mikel Apr 17 '12 at 15:27
Yes. That's why the second and following sentences of my answer are there! –  James Youngman Apr 18 '12 at 8:38
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The scheduler of a process can be defined by the programmer, using this funcion man sched_setscheduler

to see the scheduler uses by a process you can use the top command

for change the scheduler of a procces chrt

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