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

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Date:	Thu, 19 Apr 2007 08:38:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Nick Piggin <npiggin@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	William Lee Irwin III <wli@...omorphy.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:

> > And yes, by fairly, I mean fairly among all threads as a base 
> > resource class, because that's what Linux has always done
> 
> 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.
> 
> Under current kernels, that gzip will take ages and the httpds will 
> take a 1% slowdown, which may well be exactly the behaviour which is 
> desired.
> 
> If we were to schedule by UID then the gzip suddenly gets 50% of the 
> CPU and those httpd's all take a 50% hit, which could be quite 
> serious.
> 
> That's simple to fix via nicing, but people have to know to do that, 
> and there will be a transition period where some disruption is 
> possible.

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.)

	Ingo
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