ARSC HPC Users' Newsletter 234--Bulletin, December 10, 2001

SV1ex In Production at ARSC

The memory subsystem on ARSC's 32-processor SV1e, chilkoot, was upgraded to Cray's "X" memory last Saturday. This makes chilkoot the first SV1ex in production.

The single CPU memory bandwidth has increased by about 40%, the overall system bandwidth by about 90%. Almost all user codes will realize performance improvement from this upgrade, and memory intensive vector codes can expect to see significant speedup.

The upgrade is quantified, below, using the standard benchmark for measuring raw CPU to memory bandwidth, the STREAM Benchmark (see: http://www.streambench.org/). Both runs were performed on an otherwise idle system. The results are for one of the four STREAM kernels, "Triad."


       STREAM "Triad" Memory Bandwidth
  
  NCPUs   SV1e Bandwidth   SV1ex Bandwidth
             (MB/s)            (MB/s) 
  =====   ==============   ===============
     1         2504              3496
     2         4990              6886
     4         9891             13652
     8        18888             26758
    12        23266             34223
    16        25372             40690
    20        25296             44025
    24        25389             46134
    28        25528             47342
    32        25357             48177

The next table reformulates the results. It gives the increasing bandwidth available to a multitasked job as the number of CPUs is increased, as a factor of the bandwidth available on 1 CPU. Note that the SV1ex achieves a higher multiple and that the rate of increase never plateaus.


 STREAM "Triad" Memory Bandwidth Increase
  as a factor of single CPU bandwidth
  
  NCPUs       SV1e             SV1ex 
  =====   ==============   ===============
     1         1.00            1.00
     2         1.99            1.96
     4         3.95            3.90
     8         7.54            7.65
    12         9.29            9.78
    16        10.13           11.63
    20        10.10           12.59
    24        10.13           13.19
    28        10.19           13.54
    32        10.12           13.78

Watch ARSC's HPC Users' Newsletter for further discussion of the SV1ex, performance of user codes, and optimization techniques. We encourage ARSC users to share their results as they take advantage of this upgrade.


Current Editors:
Ed Kornkven ARSC HPC Specialist ph: 907-450-8669
Kate Hedstrom ARSC Oceanographic Specialist ph: 907-450-8678
Arctic Region Supercomputing Center
University of Alaska Fairbanks
PO Box 756020
Fairbanks AK 99775-6020
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