CCM/MP-2D benchmark. CCM/MP-2D is the massively parallel implementation of version 3.6.6 of the Community Climate Model (CCM). It was developed originally to determine how best to parallelize the CCM, and the results from this research are being used in the parallelization of the Community Atmoshperic Model (CAM). CCM/MP-2D is currently used for benchmarking parallel systems.

For our configuration experiments, we ran a series of experiments using two different problem sizes:

• T42L18, representing a 128x64x18 computational grid
• T170L18, representing a 512x256x18 computational grid

First, runs were made using 1, 2, 4, 8, 16, and 32 processors on a 32-processor p690. Timings were made using

• the default mapping of processes to processors
• binding processes to consecutive processors, starting with processor 0 (block mapping)
• binding processes to every other processor, starting with processor 0 (alternating mapping)
• running within an 8-processor LPAR, which forces a block mapping when using 8 processes.

The alternating mapping represents the performance that would be seen on an "HPC" version of the p690, where the Multichip Module (MCM) only has 4 processors and processors do not share L2 caches.

From these results, CCM/MP-2D performance is improved by at most 15% by using the alternating mapping instead of the block mapping. While efficiency has dropped to 50% when using 32 processes, this does not appear to be a problem that can be attributed to L2 cache sharing. For more details on the sources of performance loss for this code, go here.