linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Message-ID: <alpine.LFD.0.98.0704221620310.9964@woody.linux-foundation.org>
Date:	Sun, 22 Apr 2007 16:24:47 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Juliusz Chroboczek <jch@....jussieu.fr>
cc:	Con Kolivas <kernel@...ivas.org>, Ingo Molnar <mingo@...e.hu>,
	ck list <ck@....kolivas.org>, Bill Davidsen <davidsen@....com>,
	Willy Tarreau <w@....eu>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44

On Sun, 22 Apr 2007, Juliusz Chroboczek wrote:
> 
> Why not do it in the X server itself?  This will avoid controversial
> policy in the kernel, and have the added advantage of working with
> X servers that don't directly access hardware.

It's wrong *wherever* you do it.

The X server should not be re-niced. It was done in the past, and it was 
wrogn then (and caused problems - we had to tell people to undo it, 
because some distros had started doing it by default).

If you have a single client, the X server is *not* more important than the 
client, and indeed, renicing the X server causes bad patterns: just 
because the client sends a request does not mean that the X server should 
immediately be given the CPU as being "more important". 

In other words, the things that make it important that the X server _can_ 
get CPU time if needed are all totally different from the X server being 
"more important". The X server is more important only in the presense of 
multiple clients, not on its own! Needing to renice it is a hack for a bad 
scheduler, and shows that somebody doesn't understand the problem!

		Linus
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