On Thu, Jun 15, 2006 at 01:17:06PM -0700, Garrett D'Amore wrote:
> Wouldn't those 4- or 6- (or more!) port cards generally have working
> FIFOs on them?

Working FIFOs or not, it takes a certain amount of time to process
the interrupts and read the data.  It's hard to guess the effect
of any changes in an optimized system.  In some cases, just adding
unexecuted code in the right place can shuffle things around to
perturb the instruction cache footprint.  So you might end up with
N+1 parts of your critical path that lie in the same location in
your N-way instruction cache.  Or something else.

This is why it would be nice to be able to measure the change in
a real setup or three.  Actually, if you have a 4-port card, can
you do some tests using one port as source and the other as sink?
Maybe you could measure the execution time in cycles of the h/w
interrupt routines before and after the change.  Do you have access
to a cycle counter?

As Charles said, maybe the 4-6 modems on a 486 is not that interesting
anymore, but it would be nice to get some measurement instead of
a bunch of paper analysis or hand-waving.

So I think Pavel's setup is worth testing, but not just for operation,
but also for the amount of system time it takes to do some specific
operations.  Or, better, some measure like clock cycles/interrupt with
old code and new.

-allen

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