[Beowulf] Barcelona numbers

[Greg Lindahl]

On Tue, Sep 11, 2007 at 03:32:29AM +0000, richard.walsh at comcast.net wrote:

> So with all 8 cores at work from 2 sockets you are seeing 70% of peak assuming
> you are using 667 MHz DDR2

I'm not sure what this word "peak" means -- it cannot be achieved by
any test under any circumstances, whereas for a processor floating
point peak, you can usually do it with some weird code.

Much better to call the measured STREAM number the actual peak; then I
won't have to let loose the memory bandwidth peak bot complainer once
again ;-)

> I thought first byte latencies were around 65 nanos for Opteron.  Am
> I confused?  

You're misremembering. Opteron latency was always a function of the
number of active sockets, and it is usually measured with only one
core active, while Bill is doing the more realistic thing of having
all the cores active. Run the same code on your favorite Intel if you
want to compare.

-- greg