[Beowulf] Correct Units for quoting Interconnect Bandwidth ?

Dan Kidger daniel.kidger at quadrics.com
Fri May 28 08:36:37 EDT 2004


I have spotted an anomaly when comparing b_eff results with PMB:
   http://www.hlrs.de/organization/par/services/models/mpi/b_eff/
   http://www.pallas.com/e/products/pmb/

The former uses 1.e6 when displaying 'MBytes/s', where that latter appears to 
use 2^20.   (aka 'Mebibytes/s')
viz from PMB's Output.c:

static double MEGA = 1.0/1048576.0;
if( tmax > 0. ) throughput = (Bmark->scale_bw*SCALE*MEGA)*size/tmax;
SCALE=1000000 (declare.h)
size is in bytes, tmax in usec, and scale_bw=2 if say doing PingPong 

The result is that PMB figures appear *lower* than equivalent b_eff figures.


Do we have a concensus of what units we should be using?

So does a 1GB/s interconnect transfer 1 Gigabyte in a second or 1,000,000,000 
bytes in a second? (As interconnects move from Kilo though Mega to Giga  the 
gap is of course widening)


-- 
Yours,
Daniel.

--------------------------------------------------------------
Dr. Dan Kidger, Quadrics Ltd.      daniel.kidger at quadrics.com
One Bridewell St., Bristol, BS1 2AA, UK         0117 915 5505
----------------------- www.quadrics.com --------------------




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