[Beowulf] Lowered latency with multi-rail IB?

[Greg Lindahl]

On Thu, Mar 26, 2009 at 11:32:23PM -0400, Dow Hurst DPHURST wrote:

> We've got a couple of weeks max to finalize spec'ing a new cluster.  Has 
> anyone knowledge of lowering latency for NAMD by implementing a 
> multi-rail IB solution using MVAPICH or Intel's MPI?

Multi-rail is likely to increase latency.

BTW, Intel MPI usually has higher latency than other MPI
implementations.

If you look around for benchmarks you'll find that QLogic InfiniPath
does quite well on NAMD and friends, compared to that other brand of
InfiniBand adaptor. For example, at

http://www.ks.uiuc.edu/Research/namd/performance.html

the lowest line == best performance is InfiniPath. Those results
aren't the most recent, but I'd bet that the current generation of
adaptors has the same situation.

-- Greg
(yeah, I used to work for QLogic.)