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
