The only way I got under 1usec in PingPong test or with ib_[write/send/read]_lat is with QDR and back to back (ie. no switch). With switch I get 1.1[3-7]usec [HP-MPI, OpenMPI, MVAPICH]. It does not matter the MPI although I have to agree with Greg that multirail also increases latency. Multirail is used for: i) reliability ii) higher bandwidth
Best regards, Joshua ------ Original Message ------ Received: 11:11 PM CDT, 03/26/2009 From: Greg Lindahl <[email protected]> To: [email protected] Subject: Re: [Beowulf] Lowered latency with multi-rail IB? > 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.) > > _______________________________________________ > Beowulf mailing list, [email protected] > To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf > _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
