[ofa-general] Expected RDMA performance

[Peter Kjellstrom]

On Friday 19 October 2007, Michael Krause wrote:
> At 08:20 AM 10/19/2007, Peter Kjellstrom wrote:
> >On Thursday 18 October 2007, Chuck Hartley wrote:
...
> > > What is the maximum theoretical BW for
> > > DDR IB - 1525MB/sec?
> >
> >No, it's 20 Gbps on the wire and 8/10 encoded so 16 Gbps effective which
> > is 2000 MB/s (10-base) and 1907 MiB/s (2-base).
>
> There is also IB protocol overhead combined with driver / device control
> traffic overhead (consumes device as well as PCI resources / bandwidth),
> end-to-end control traffic  which is also a function of how the application
> is constructed.   In general, hitting about 80-85% of the theoretical
> maximum is possible.

IB can do much better than that. On an SDR system I typically get 950 MB/s 
(10-base), 95%. This on 8x pci-express so the limitations of pci-e above does 
not bite. If IB DDR could strech it's legs (if we had faster pci-e, say 
pci-e-2.0...) then maybe we would see 95% there too :-).

/Peter
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