Re: SCHED_IDLE documentation

[Ingo Molnar <mingo@elte.hu>]

* Michael Kerrisk <mtk.manpages@googlemail.com> wrote:

> On Mon, Mar 3, 2008 at 8:33 AM, Ingo Molnar <mingo@elte.hu> wrote:
> >
> > * Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > > If we don't have any man page, what is the actual definition of
> > > SCHED_IDLE anyway?
> >
> > it's rather simple: "it's a priority level even lower priority than nice
> > +19".
> 
> Some other questions whose answers may be worth including in the man page:
> 
> * When was SCHED_IDLE added?  (Actually, who added it?)

"git-blame include/linux/sched.h" gives you that information, it was 
added by me as part of CFS:

  commit 0e6aca43e08a62a48d6770e9a159dbec167bf4c6
  Author: Ingo Molnar <mingo@elte.hu>
  Date:   Mon Jul 9 18:51:57 2007 +0200

      sched: add SCHED_IDLE policy
 
> * Why was it added?  (What are the particular benefits of the new 
> sceuling class as opposed to using a very low nice value for 
> SCHED_OTHER?)

because some people wanted even lower priorities than what nice +19 
gave, and extending nice levels wasnt possible for ABI reasons.

> * What's the difference between SCHED_IDLE and SCHED_BATCH?

SCHED_BATCH can still have nice levels from -20 to +19, it is a modified 
SCHED_OTHER/SCHED_NORMAL for "throughput oriented" workloads.

SCHED_IDLE overrides the nice settings and it means a "super idle" 
workload.

	Ingo