[Beowulf] Woodcrest Memory bandwidth

John Cutonilli jcutonilli at haifire.com
Mon Aug 14 19:52:35 EDT 2006


I have an older system, but I thought the results were interesting.

ifort -O3 -static  stream.f mysecond.o
Function     Rate (MB/s)  Avg time   Min time  Max time
Copy:       2874.5953      0.0113      0.0111      0.0115
Scale:      2864.0447      0.0114      0.0112      0.0125
Add:        3467.2027      0.0143      0.0138      0.0172
Triad:      3471.2678      0.0142      0.0138      0.0150

ifort -O3 -static -xN stream.f mysecond.o
Function     Rate (MB/s)  Avg time   Min time  Max time
Copy:       4102.0088      0.0079      0.0078      0.0084
Scale:      4100.8808      0.0079      0.0078      0.0082
Add:        4437.9277      0.0110      0.0108      0.0112
Triad:      4431.2855      0.0110      0.0108      0.0112

It's pretty interesting the difference a small change to the compiler
options will give.

The 10 GB/s number may be a reference to the 10.5 GB/s maximum bandwidth per
processor the Woodcrest 1333 MHz FSB cpus are theoretically capable of
achieving. This is in contrast to the 6.4 GB/s numbers for the Opterons and
older Intels (PC-3200)

John Cutonilli

> Bill and I passed a few emails off the list and it seems that he's heard
> reports of up to 10 GB/s.  I tried on 2 different Woodcrest systems (one
> from Dell, one directly from Intel) here and they both report back
> similar numbers.  It seems that the fortran version of the program with
> pathscale 2.3 (the numbers I reported above) reports different numbers
> than the C version of the program with pathscale 2.3:
> 
> Function      Rate (MB/s)   Avg time     Min time     Max time
> Copy:        6129.2441       0.2090       0.2088       0.2097
> Scale:       6138.1509       0.2087       0.2085       0.2091
> Add:         5935.6727       0.3236       0.3235       0.3237
> Triad:       5972.4347       0.3217       0.3215       0.3221
> 
> and the C version with Intel 9.1:
> 
> Function      Rate (MB/s)   Avg time     Min time     Max time
> Copy:        6145.6340       0.2084       0.2083       0.2090
> Scale:       4830.1172       0.2652       0.2650       0.2658
> Add:         5289.7542       0.3632       0.3630       0.3638
> Triad:       5296.5246       0.3629       0.3625       0.3640
> 
> Thanks,
> 
> --
> Jason Holmes


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