Ok, so the latencies for the MPI call stack, even without the thread locks, is greater than we'd like.  To get the desired message rate, we'll also need to improve that.  Do these tests turn off the error checking?  Would it be possible to run the tests with a return instead of a function call at various levels?  Since the operations are basically no-ops, we (ie, Pavan) could then easily measure the contribution of each layer, without worrying about the cost of instrumentation.  (This is less important than getting some more thread results, but it will be helpful in guiding any more substantive code changes).

Bill

On Jan 31, 2008, at 9:36 AM, Pavan Balaji wrote:


Ah, I had missed the fact that it didn't scale the results.  So is the cost of the MPI call stack to the top of the ch3 code (where the proc-null test is) about 25ns on Breadboard and 60ns on BG/P?

No. The latency number is already total_time / (LOOPS * 16), so you can't divide the latency number by 16 again.

Sorry for the confusion.

 -- Pavan

-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji


William Gropp
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign