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Subject: Re: [OMPI users] TCP Latency
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-07-28 14:59:51


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

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; are those iWARP-capable cards?

-- 
Jeff Squyres
Cisco Systems