Performance Studies using PSTSWM

Compaq AlphaServer SC Serial Performance

(comparing performance when running multiple instances)

(fixed problem size per processor)

T42 MFlop rates

Per Processor Rate	Per Node Rate

T85 MFlop rates

Per Processor Rate	Per Node Rate

T170 MFlop rates

Per Processor Rate	Per Node Rate

DISCUSSION

• The performance discrepancy here indicates the cost of contention for memory (bandwidth) when multiple processors are running simultaneously. The total memory required per node goes up as the number of processors increases, but the per processor cache behavior and memory access patterns is constant.
• This experiment indicates the difference in performance one might see in a space sharing context, sharing the node with other users, or in a scaled speed-up experiment, where the size of a parallel job is increased as the number of processors used increases.
• Note that two different metrics are displayed - per processor computational rate and per node computational rate. The per node rate is the best measure of the performance of the architecture, but the per processor rate is a convenient way to observe performance degradation.
• Summary: Per processor performance degrades as the number of processors used per node increases for all cases but the smallest (T42L1). The performance difference between 1 processor and 4 processors per node is fairly consistent, ranging from 50-100 MFlops/sec in most cases, with the 2 and 3 processor rates showing approximately one third and two thirds of the degradation of the 4 processor rate, respectively. Note, however, that it never makes sense to use less than 4 processors per node when looking at per node computational rates.

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Patrick H. Worley / ( worleyph@ornl.gov)
Last Modified Monday, 15-Jul-2002 10:03:24 EDT.
3167 accesses since 1/2/96.