[ofa-general] Expected RDMA performance

[Peter Kjellstrom]

On Monday 22 October 2007, Michael Krause wrote:
...
> > > 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 :-).
>
> While there are certainly marketing workloads that can hit such high
> efficiencies, the number of real world workloads is rather small.

Wow, slow down. Who said real workloads? And what is a real workload anyway?

I don't care since that wasn't the issue here. The OP asked about ib_write_bw 
(or similar) _not_ what you could expect running some random application. My 
answer included comments on how his figures matched his hardware, a bit on 
why he didn't see 1907 MiB/s etc.

I think that nicely ends this thread.

/Peter
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