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From: Robert Dewar <robert_dewar@my-dejanews.com>
Subject: Re: Context Switching
Date: 1999/05/11
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References: <m3_X2.48$6o.1372369@news.siol.net>
 <rracine.11.00086657@draper.com> <3736e104@eeyore.callnetuk.com>
 <37383ab3@eeyore.callnetuk.com>
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Date: 1999-05-11T00:00:00+00:00
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In article <37383ab3@eeyore.callnetuk.com>,
  "Nick Roberts" <nickroberts@callnetuk.com> wrote:
> In another thread I said some processors could do a context
switch in a few
> 'picoseconds'.  I am grateful to Keith Thompson pointing out
to me that I
> meant 'nanoseconds'.  It'll happen one day, of course, but not
until they've
> solved the problem of those pesky tunnelling electrons.
Sorry!


You have to be careful here. The raw hardware speed for a
context switch is not what is interesting, what is interesting
is the time for executing the COMPLETE pthread call that causes
the context switch.

For example, the actual raw hardware speed for changing a task
priority is probably just a single store instruction, but it may
well take hundreds or even thousands of instructions to filter
through the necessary kernel machinery to get to the point of
issuing that store!


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