Re: Can context switches be faster?

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Chris Friesen wrote:
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.


That's a load more descriptive :D

0.890 uS, 0.556uS/cycle, that's barely 2 cycles you know. (Pentium M)
PPC performs similarly, 1 cycle should be about 1uS.

Chris


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