Re: MMX performance....

Dale R. Worley (
Thu, 6 Feb 1997 13:31:10 GMT

In article <> Phillip G Ezolt <> writes:
From what I understand, everytime you switch between MMX mode and regular
FP mode, 100 or so cycles are burned. If you are context switching
alot (any multitasking enviornment), this would seem to add up.

Assuming that the "cycles" are fundamental CPU cycles (as opposed to
memory accesses, or something), that could take 1 microsecond or less
(depending on your clock speed), which isn't much. Even better, if
you arrange that the kernel doesn't use either FP or MMX, then MMX/FP
switches can only happen when switching user processes, which is
fairly infrequent -- and the MMX/FP switchover overhead is probably
much smaller than the scheduler overhead.


Dale R. Worley					Ariadne Internet Services
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