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

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Date:	Thu, 19 Apr 2007 00:57:46 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	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]

* 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

-- wli
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