Re: Can context switches be faster?

Chris Friesen
2006-10-12T19:58:10Z

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