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

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Message-ID: <452EA441.6070703@comcast.net>
Date:	Thu, 12 Oct 2006 16:23:29 -0400
From:	John Richard Moser <nigelenki@...cast.net>
To:	Chris Friesen <cfriesen@...tel.com>
CC:	linux-kernel@...r.kernel.org
Subject: 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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