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From: Peter Kjellstrom (cap_at_[hidden])
Date: 2007-01-18 05:05:07


On Thursday 18 January 2007 09:52, Robin Humble wrote:
...
> is ~10Gbit the best I can expect from 4x DDR IB with MPI?
> some docs @HP suggest up to 16Gbit (data rate) should be possible, and
> I've heard that 13 or 14 has been achieved before. but those might be
> verbs numbers, or maybe horsepower >> 4 cores of 2.66GHz core2 is
> required?

The 16 Gbit/s number is the theoretical peak, IB is coded 8/10 so out of the
20 Gbit/s 16 is what you get. On SDR this number is (of course) 8 Gbit/s
achievable (which is ~1000 MB/s) and I've seen well above 900 on MPI (this on
8x PCIe, 2x margin).

The same setup on 4x PCIe stops at a bit over 700 MB/s (for a certain PCIe
chipset) so it makes some sense that an IB 4x DDR on 8x PICe would be limited
to about 1500 MB/s (on that platform). All this ignoring possible MPI bottle
necks above 900 MB/s and assuming the IB fabric can reach 95%+ of peak on DDR
as it does on SDR...

/Peter



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