linux-kernel - Re: SCHED_IDLE documentation

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Date:	Mon, 3 Mar 2008 11:03:56 +0100
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Arnd Bergmann" <arnd@...db.de>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Christoph Hellwig" <hch@....de>,
	cbe-oss-dev@...abs.org, "Jeremy Kerr" <jk@...abs.org>,
	linux-kernel@...r.kernel.org
Subject: Re: SCHED_IDLE documentation

On Mon, Mar 3, 2008 at 10:31 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Monday 03 March 2008, Ingo Molnar wrote:
> > > * 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.
>
> Does that mean that a SCHED_IDLE task still runs some of the time if
> you have a CPU hog running on +19, or can any other process starve the
> SCHED_IDLE task?

Thanks.  That was going to be my next question!

I'm guessing that SCHED_IDLE doesn't get completely starved by a CPU
hog running nice +19, but it would still be interesting to know:
roughly how much of the CPU could the CPU_IDLE process expect to get
in that case?

> What happens if you have two SCHED_IDLE tasks on a single CPU, do they get
> equal share, or will they just run as batch jobs?

Also might be useful to add th e answer to this to the man page...

Cheers,

Michael


-- 
Michael Kerrisk
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