Hi Roberto. We've had strange reports of performance from EC2 before; it's actually been on my to-do list to go check this out in detail. I made contact with the EC2 folks at Supercomputing late last year. They've hooked me up with some credits on EC2 to go check out what's happening, but the pent-up email deluge from the Christmas vacation and my travel to the MPI Forum this week prevented me from testing yet.
I hope to be able to get time to test Open MPI on EC2 next week and see what's going on. It's very strange to me that Open MPI is getting *better* than raw TCP performance. I don't have an immediate explanation for that -- if you're using the TCP BTL, then OMPI should be using TCP sockets, just like netpipe and the others. You *might* want to check hyperthreading and process binding settings in all your tests. On Jan 12, 2012, at 7:04 AM, Roberto Rey wrote: > Hi again, > > Today I was trying with another TCP benchmark included in the hpcbench suite, > and with a ping-pong test I'm also getting 100us of latency. Then, I tried > with netperf and the same result.... > > So, in summary, I'm measuring TCP latency with messages size between 1-32 > bytes: > > Netperf over TCP -> 100us > Netpipe over TCP (NPtcp) -> 100us > HPCbench over TCP -> 100us > Netpipe over OpenMPI (NPmpi) -> 60us > HPCBench over OpenMPI -> 60us > > Any clues? > > Thanks a lot! > > 2012/1/10 Roberto Rey <eros...@gmail.com> > Hi, > > I'm running some tests on EC2 cluster instances with 10 Gigabit Ethernet > hardware and I'm getting strange latency results with Netpipe and OpenMPI. > > If I run Netpipe over OpenMPI (NPmpi) I get a network latency around 60 > microseconds for small messages (less than 2kbytes). However, when I run > Netpipe over TCP (NPtcp) I always get around 100 microseconds. For bigger > messages everything seems to be OK. > > I'm using the BTL TCP in OpenMPI, so I can't understand why OpenMPI > outperforms raw TCP performance for small messages (40us of difference). I > also have run the PingPong test from the Intel Media Benchmarks and the > latency results for OpenMPI are very similar (60us) to those obtained with > NPmpi > > Can OpenMPI outperform Netpipe over TCP? Why? Is OpenMPI doing any > optimization in BTL TCP? > > The results for OpenMPI aren't so good but we must take into account the > network virtualization overhead under Xen > > Thanks for your reply > > > > -- > Roberto Rey Expósito > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
