Hi Alex. one Question - additional to Yankees question: Did you ensure to use the same overall problem size? In the example code, the problem sizes increases linear with the number of processes - in this case, a single process still has to do the same amount of work - additional to the communication. Than, of course, you will not see any speedup. Lena On May 19, 2016, at 12:33 PM, Guo, Yanfei <[email protected]<mailto:[email protected]>> wrote: Hi Alex, On 5/18/16, 6:26 PM, "Alexandre Vieira" <[email protected]<mailto:[email protected]>> wrote: Hello list, I'm currently writing a paper on distributed computing and also elaborate a simple use case to include as a proof of concept. My setup: - 3 VMs running on different machines (same HW) with 1 CPU and 2GB RAM running FreeBSD 10.3 - Connected through a 1Gbps LAN and communicate passwordless through SSH. - MPICH 3.2_1 installed and working on the three nodes I've tried to compile and run some code samples that are available for mpich (i.e: http://people.sc.fsu.edu/~jburkardt/c_src/mpi/search_mpi.c) but I always end up getting worst times running on the 3 nodes that I get running on 1 node alone, even when I can get all 3 nodes to get up to a 100% CPU usage for a couple of minutes. How much slower? When you say running on 1 node, do you mean all three VMs are on the same physical machine, or just running a serial implementation of the program? How many CPU cores does the physical machine have? I know there is network overhead and SSH isn't helping either, so without investing too much time I unfortunately won't have, I'd like to ask you what kind of simple program could I write just for the sake of a proof of concept that running a program with 3 nodes would be faster than running on one. Network latency could be a problem because the communication goes through memory when all processes/VMs are on the same physical machine, which is way faster then Ethernet. Maybe dealing with slower operations like disk I/O do counter the inter-node communication? It is unlikely that disk I/O has something to do with this. Many thanks for your kind help BR Alex Yanfei Guo Postdoctoral Researcher MCS Division, ANL _______________________________________________ discuss mailing list [email protected]<mailto:[email protected]> To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss