Message-ID: <452E9E47.8070306@nortel.com>
Date: Thu, 12 Oct 2006 13:57:59 -0600
From: "Chris Friesen" <cfriesen@nortel.com>
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To: John Richard Moser <nigelenki@comcast.net>
CC: linux-kernel@vger.kernel.org
Subject: Re: Can context switches be faster?
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John Richard Moser wrote:

> Linux ported onto the L4-Iguana microkernel is reported to be faster
> than the monolith[1]; it's not like microkernels are faster, but the
> L4-Iguana apparently just has super awesome context switching code:
> 
>    Wombat's context-switching overheads as measured by lmbench on an
>    XScale processor are up to thirty times less than those of native
>    Linux, thanks to Wombat profiting from the implementation of fast
>    context switches in L4-embedded.

The Xscale is a fairly special beast, and it's context-switch times are 
pretty slow by default.

Here are some context-switch times from lmbench on a modified 2.6.10 
kernel. Times are in microseconds:

cpu		clock speed	context switch	
pentium-M	1.8GHz		0.890
dual-Xeon	2GHz		7.430
Xscale		700MHz		108.2
dual 970FX	1.8GHz		5.850
ppc 7447	1GHz		1.720

Reducing the Xscale time by a factor of 30 would basically bring it into 
line with the other uniprocessor machines.

Chris
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