[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:

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)


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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