Re: [OMPI users] TCP Latency

[George Bosilca]

I just want to make sure that I correctly understand your statement. You're saying that running NetPIPE (NPtcp) directly over TCP give you a latency of 12us, but running NetPIPE (NPmpi) over Open MPI bring this latency up to 45us ?

  george.

On Jul 29, 2008, at 10:52 AM, Andy Georgi wrote:

Zitat von Jeff Squyres <jsquy...@cisco.com>:

On Jul 28, 2008, at 2:53 PM, Andy Georgi wrote:

we use Chelsio S320E-CXA adapters (http://www.chelsio.com/assetlibrary/products/S320E%20Product%20Brief%20080424.pdf )

in one of our clusters. After tuning the kernel i measured the ping

think. So i wrote a simple ping-pong-kernel and was really terrified
about the ~45us i got with OpenMPI 1.2.6. Are there any hints how we
can reduce the MPI latency? To increase the bandwidth we already set
the buffer sizes but we couldn't find a parameter which can be
relevant for the latency. Every hint is  welcome.

pong latency via NetPIPE and got ~12us which is pretty good for TCP i

are those iWARP-capable cards?

The upcoming Open MPI v1.3 series will support iWARP, which gives much better latency than that. I don't know all the Chelsio models offhand;

Thanks for the fast answer. So is this latency normal for TCP
communications over MPI!? Could RDMA maybe reduce the latency? It
should work with those cards but there are still problems with OFED.
iWARP is also one of the features they offer but if it works...

--

Dresden University of Technology
Center for Information Services
and High Performance Computing (ZIH)
D-01062 Dresden
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e-mail: andy.geo...@zih.tu-dresden.de
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