linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Date:	Fri, 20 Apr 2007 16:16:56 +1000
From:	Peter Williams <pwil3058@...pond.net.au>
To:	William Lee Irwin III <wli@...omorphy.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, Mike Galbraith <efault@....de>,
	Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>,
	Bill Huey <billh@...ppy.monkey.org>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair
 Scheduler [CFS]

William Lee Irwin III wrote:
> William Lee Irwin III wrote:
>>> I'd further recommend making priority levels accessible to kernel threads
>>> that are not otherwise accessible to processes, both above and below
>>> user-available priority levels. Basically, if you can get SCHED_RR and
>>> SCHED_FIFO to coexist as "intimate scheduler classes," then a SCHED_KERN
>>> scheduler class can coexist with SCHED_OTHER in like fashion, but with
>>> availability of higher and lower priorities than any userspace process
>>> is allowed, and potentially some differing scheduling semantics. In such
>>> a manner nonessential background processing intended not to ever disturb
>>> userspace can be given priorities appropriate to it (perhaps even con's
>>> SCHED_IDLEPRIO would make sense), and other, urgent processing can be
>>> given priority over userspace altogether.
> 
> On Thu, Apr 19, 2007 at 09:50:19PM +1000, Peter Williams wrote:
>> This is sounding very much like System V Release 4 (and descendants) 
>> except that they call it SCHED_SYS and also give SCHED_NORMAL tasks that 
>> are in system mode dynamic priorities in the SCHED_SYS range (to avoid 
>> priority inversion, I believe).
> 
> Descriptions of that are probably where I got the idea (hurrah for OS
> textbooks).

And long term background memory.  :-)

> It makes a fair amount of sense.

Yes.  You could also add a SCHED_IA in between SCHED_SYS and SCHED_OTHER 
(a la Solaris) for interactive tasks.  The only problem is how to get a 
task into SCHED_IA without root privileges.

> Not sure what the take on
> the specific precedent is. The only content here is expanding the
> priority range with ranges above and below for the exclusive use of
> ultra-privileged tasks, so it's really trivial. Actually it might be so
> trivial it should just be some permission checks in the SCHED_OTHER
> renicing code.

Perhaps.

Peter
-- 
Peter Williams                                   pwil3058@...pond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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