Joshua mora acosta wrote: > 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 >
What about using multi-rail to increase message rate? That isn't the same as latency, but if you put messages on both wires you should get more. A vendor tried to convince me recently that this was important, but they had no benchmarks to back it up. Craig > > ------ 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 > -- Craig Tierney ([email protected]) _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
