Estimating the Balance Point

Here we graph the simple performance model derived earlier:

MB = 48 MF/ (132 L) = 0.364 MF / L ,


  • Note that this is a log-log plot.
  • The messages vary in size from 800 bytes to 30 KB for problem sizes of interest. The arrows near the bottom of the graph correspond to different L values.
  • The green curve and lower blue curve come from measured performance on the Roadrunner supercluster at the Albuquerque High Performance Computer Center. The upper blue curve is from the Indiana University IBM SP. The red curve is from Scali (Wulfpack) and the black curve is from a Compaq Alpha SC using the Quadrics interconnect. The measurements are done using the Netpipe program from the Ames Scalable Computing Laboratory
  • The straight red lines come from the performance model presented and are plotted for matrix times vector speeds of 50, 100 and 200 MF. We need to run at a large enough value of L so that the measured bandwidth is above the red line (for what ever speed our processor achieves for the corresponding value of L).
  • Pushing up the communication rate for small messages is important.
  • It is especially nice when we don't need more expensive hardware. There is a huge price difference between Fast Ethernet and the other interconnects.



Single Node Performance (next slide)

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