It depends. If all you want is the 2 process flipping back and forth
number, it is ~5 usecs on a K6@233Mhz and ~9 usecs on P5@120Mhz.
The numbers go up dramatically as the size of the process goes up.
By orders of magnitude. Think about it: if all I am dong is context
switching then most of what I need is in the L2 cache tagged by context id
and I don't go to memory at all. So it becomes a pure CPU speed issue.
But if I'm touching data in each context, then I am throwing the other
guy's data out of the cache and he gets stalled when he sarts up again.
Unfortunately, the latter is far more common than the former.
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