Re: Cray Results for bandwidth test

From: Andrew Zachary (
Date: Mon Sep 30 1991 - 07:48:25 CDT


Your guess is correct: the optimizer is removing all those dead blocks
of code! I put each of the loops into a subroutine, turned off double
precision, and then used second to time the loops. The results now
make sense: 150 Mflops for the sum and scale, 300 Mflops for the saxpy,
and storage rates of 2400 Mbytes/sec for sum and scale and 3600 Mbytes/sec
on saxpy. Note that the 3600 Mbytes/sec figure is a bit below the
theoretical peak of 4000 Mbytes/sec for a saxpy, but I wasn't running
on a dedicated machine. Also, I had to run on a machine with only
64 Memory banks, so I may have had some unexpected bank conflicts.

I will send you a "certified" copy of the results once my machine
comes back up...

Andrew Zachary

P.S. If you would like to see the results for a dedicated 8 processor
machine, let me know. I can probably arrange the time.

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