[Beowulf] Q: IB message rate & large core counts (per node)?

[Brian Dobbins]

>   I thought PCIe Gen2 x 8 @ 500 Mhz gives 8GB/s?  I know there are 250 and
> 500 Mhz variants in addition to the lane sizes, so while a 250 Mhz x8 link
> wouldn't provide enough bandwidth to a dual-port card, the 500 Mhz one
> should.  But I'm woefully out of date on my hardware knowledge, it seems.
> Of course, EDR (eight data-rate) IB is on the roadmap for 2011, so if we're
> in no rush that could help, too.
>

Er,.. I thought about this a half-second after I sent it.  First, that's 5.0
Ghz, not 500 Mhz, and second, that's probably aggregate bi-directional
throughout at 8 GB/s, isn't it?  So, I got it, 4 GB/s per direction, which
means dual-port won't get us much in terms of unidirectional throughput.

  - Brian
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