Hi Carsten, The benchmarks were made is 1 NIC/node, and yet the scaling is bad. Does that mean that there is indeed network congestion ? We will try using back to back connections soon,
-himanshu maybe your problem is not even flow control, but the limited network bandwidth which is shared among 4 CPUs in your case. I also have done benchmarks on Woodcrests > (2.33 GHz) and was not able to scale an 80000 atom system beyond 1 node with > Gbit Ethernet. Looking in more detail, the time gained by the additional 4 > CPUs of a > second node was exactly balanced by the extra communication. I used only 1 > network interface for that benchmark, leaving effectively only 1/4 th of the > bandwidth > for each CPU. Using two interfaces with OpenMPI did not double the network > performance on our cluster. In my tests nodes with 2 CPUs sharing one NIC > were faster > than nodes with 4 CPUs sharing two NICs. Could be on-node contention, since > both interfaces probably end up on the same bus internally. > > Are the benchmarks made with 1 or 2 NICs/node? If they are for 1 NIC/node > then there should be no network congestion for the case of 8 CPUs (=2 nodes). > You could > try a back-to-back connection between two nodes to be absolutely shure that > the rest of the network (switch etc.) does not play a role. I would try that > and repeat > the benchmark for 8 CPUs. See if you get a different value. > ############## _______________________________________________ gmx-users mailing list [email protected] http://www.gromacs.org/mailman/listinfo/gmx-users Please search the archive at http://www.gromacs.org/search before posting! Please don't post (un)subscribe requests to the list. Use the www interface or send it to [EMAIL PROTECTED] Can't post? Read http://www.gromacs.org/mailing_lists/users.php
