linux-kernel - Re: SCHED_IDLE documentation

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Date:	Mon, 3 Mar 2008 13:31:54 +0100
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Arnd Bergmann" <arnd@...db.de>, "Christoph Hellwig" <hch@....de>,
	cbe-oss-dev@...abs.org, "Jeremy Kerr" <jk@...abs.org>,
	linux-kernel@...r.kernel.org
Subject: Re: SCHED_IDLE documentation

Ingo,

> > * 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.

So, suppose we have two CPU intensive jobs, one SCHED_OTHER and the
other SCHED_BATCH.  If they have the same nice value, will/should the
scheduler favour one over the other?

I've done some testing on 2.6.25-rc2, x86-32 for this case, and it
appears that the two jobs are treated the same by the scheduler (each
gets 50% of CPU).  Is that expected behavior?  If it is, can you give
an example where scheduling SCHED_OTHER versus SCHED_BATCH should show
a difference in the amount of CPU received by each process?

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

Tested on 2.6.25-rc2, x86-32.  Two CPU intensive jobs, one
SCHED_OTHER, nice=+19, the other SCHED_IDLE.  The SCHED_OTHER job gets
~88% of CPU.  So SCHED_IDLE does indeed give a "super low nice"
effect.

Cheers,

Michael

-- 
Michael Kerrisk
Maintainer of the Linux man-pages project
http://www.kernel.org/doc/man-pages/
Want to report a man-pages bug?  Look here:
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