linux-kernel - Re: Can context switches be faster?

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Date:	Thu, 12 Oct 2006 13:57:59 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	John Richard Moser <nigelenki@...cast.net>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Can context switches be faster?

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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