[Beowulf] cluster softwares supporting parallel CFD computing

Eric W. Biederman ebiederm at xmission.com
Wed Sep 6 13:10:14 EDT 2006


"Daniel Kidger" <daniel.kidger at clearspeed.com> writes:

> Bogdan,
>
> Parallel applications with lots of MPI traffic should run fine on a cluster
> with large jiffies - just as long as the interconnect you use doesn't need to
> take any interrupts. (Interrupts add hugely to the latency figure)

I know a lot of NICs misplaced interrupt mitigation adds to the latency figure.
I know people who are serious about optimizing their hardware for mpi traffic
poll for interrupts.

There is fundamentally more work to do when you take an interrupt because
you need to take a context switch.  But cost of a context switch is in
the order of microseconds, so while measurable taking an interrupt should 
not dramatically your latency numbers.

Do you have any measurements to show that interrupts add hugely to latency
figures, as opposed to a poor implementation of interrupts.

This is important as polling for new packets has a very significant opportunity
cost as it prevents you from get any other work done at the same time

Eric
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