So a way to quantify if multirail helps on network latency driven workloads there should be a sinthetic benchmark that can be built to show off the impact of balancing these requests among multiple HCAs bound to different network paths or core pairs like an all-to-[all,gather,scatter] or barrier benchmark and in theory observe half the total latency of that overall communication. So I think multirail will reduce latency of sinchronizations (collective calls) but not to latency driven point to point communications.
Joshua ------ Original Message ------ Received: 12:37 PM CDT, 03/27/2009 From: Håkon Bugge <[email protected]> To: Craig Tierney <[email protected]>Cc: Joshua mora acosta <[email protected]>, [email protected], [email protected] Subject: Re: [Beowulf] Lowered latency with multi-rail IB? > On Mar 27, 2009, at 18:20 , Craig Tierney wrote: > > > 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. > > Exactly why we saw almost 2x speedup on message rate (latency) > sensitive apps using Platform MPI. We call the technique alternating; > any communicating peer will use a HCA or port, but a single MPI > process will alternate between different HCAs (or ports), depending on > which peer he communicates with. > > > Håkon _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
