[Beowulf] New beowulf recommendations

Geoff Jacobs gdjacobs at gmail.com
Sun Sep 9 20:12:40 EDT 2007


Mark Hahn wrote:
> well, the simplest test is to connect two nodes back-to-back and run a
> latency test.  compare versus plugged into the switch.
> (gigabit ports are all auto-mdi, so you don't need a special crossover
> cable for this test.)
> 
> I would guess that your current switch is about the same latency as the
> GSM7248, but that you'll measure something like 50 us back-to-back.  so
> dropping 18 us will not make a dramatic difference:
> ie, 70 us vs 52 - that's 25%, but it's still no where near a "real"
> interconnect (myrinet, infiniband, 10G, quadrics).
> 
> you should also verify that your nics aren't currently doing some sort
> of interrupt mitigation/coalescing, since that will hurt your latency.
> 
> if you are truely small-packet latency-bound, and unwilling to consider
> a higher-performance interconnect, I think you should contemplate putting
> more cores in each box.  going from 2 cores per box to 8 or 16 will make a
> big difference for smallish jobs that use a small number of nodes (even
> if you stick to plain old gigabit).

What is GAMMA like for stability these days? It's efficiency would be
compelling enough for me to do some testing, at least, were I in this
situation. Going this route would also make switch latency somewhat more
relevant.

-- 
Geoffrey D. Jacobs

To have no errors
  would be life without meaning
  No struggle, no joy
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