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

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Date:	Sun, 22 Apr 2007 06:58:53 +0200
From:	Mike Galbraith <efault@....de>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	Denis Vlasenko <vda.linux@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, Willy Tarreau <w@....eu>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.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, 2007-04-22 at 10:08 +1000, Con Kolivas wrote:
> On Sunday 22 April 2007 08:54, Denis Vlasenko wrote:
> > On Saturday 21 April 2007 18:00, Ingo Molnar wrote:
> > > correct. Note that Willy reniced X back to 0 so it had no relevance on
> > > his test. Also note that i pointed this change out in the -v4 CFS
> > >
> > > announcement:
> > > || Changes since -v3:
> > > ||
> > > ||  - usability fix: automatic renicing of kernel threads such as
> > > ||    keventd, OOM tasks and tasks doing privileged hardware access
> > > ||    (such as Xorg).
> > >
> > > i've attached it below in a standalone form, feel free to put it into
> > > SD! :)
> >
> > But X problems have nothing to do with "privileged hardware access".
> > X problems are related to priority inversions between server and client
> > processes, and "one server process - many client processes" case.
> 
> It's not a privileged hardware access reason that this code is there. This is 
> obfuscation/advertising to make it look like there is a valid reason for X 
> getting negative nice levels somehow in the kernel to make interactive 
> testing of CFS better by default.

That's not a very nice thing to say, and it has no benefit unless you
specifically want to run multiple heavy X hitting clients.

I boot with that feature disabled specifically to be able to measure
fairness in a pure environment, and it's still _much_ smoother and
snappier than any RSDL/SD kernel I ever tried.

	-Mike

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