linux-kernel - Re: [PATCH] CFS: Fix missing digit off in wmult table

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Message-ID: <20070716203117.GC11166@waste.org>
Date:	Mon, 16 Jul 2007 15:31:18 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Ingo Molnar <mingo@...e.hu>, James Bruce <bruce@...rew.cmu.edu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH] CFS: Fix missing digit off in wmult table

On Mon, Jul 16, 2007 at 04:01:17PM +0200, Roman Zippel wrote:
> Hi,
> 
> On Mon, 16 Jul 2007, Ingo Molnar wrote:
> 
> > to sum it up: a nice +19 task (the most commonly used nice level in 
> > practice) gets 9.1%, 3.9%, 3.1% of CPU time on the old scheduler, 
> > depending on the value of HZ. This is quite inconsistent and illogical.
> 
> You're correct that you can find artifacts in the extreme cases, it's 
> subjective whether this is a serious problem.
> It's nice that these artifacts are gone, but that still doesn't explain 
> why this ratio had to be increase that much from around 1:10 to 1:69.

More dynamic range is better? If you actually want a task to get 20x
the CPU time of another, the older scheduler doesn't really allow it.

Getting 1/69th of a modern CPU is still a fair number of cycles.
Nevermind 1/69th of a machine with > 64 cores.

-- 
Mathematics is the supreme nostalgia of our time.
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