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

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Date:	Thu, 19 Apr 2007 21:50:19 +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:
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
>>> Yes, there are potential compatibility problems.  Example: a machine 
>>> with 100 busy httpd processes and suddenly a big gzip starts up from 
>>> console or cron.
> [...]
> 
> On Thu, Apr 19, 2007 at 08:38:10AM +0200, Ingo Molnar wrote:
>> hmmmm. How about the following then: default to nice -10 for all 
>> (SCHED_NORMAL) kernel threads and all root-owned tasks. Root _is_ 
>> special: root already has disk space reserved to it, root has special 
>> memory allocation allowances, etc. I dont see a reason why we couldnt by 
>> default make all root tasks have nice -10. This would be instantly loved 
>> by sysadmins i suspect ;-)
>> (distros that go the extra mile of making Xorg run under non-root could 
>> also go another extra one foot to renice that X server to -10.)
> 
> 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.
> 
> I believe root's default priority can be adjusted in userspace as
> things now stand somewhere in /etc/ but I'm not sure of the specifics.
> Word is somewhere in /etc/security/limits.conf

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).

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

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