Re: Can context switches be faster?

John Richard Moser
2006-10-12T20:23:33Z

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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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