Thank you for your fast response.


I am launching 200 light processes in two computers with 8 cores each one (Intel i7 processor). They are dedicated and are interconnected through a point-to-point Gigabit Ethernet link.


I read about oversubscribing nodes in the open-mpi documentation, and for that reason I am using the option


-    Mca mpi_yield_when_idle 1








>>On Feb 29, 2012, at 11:01 AM, Pinero, Pedro_jose wrote:


>> I am using OMPI v.1.5.5 to communicate 200 Processes in a 2-Computers cluster connected though Ethernet, obtaining a very poor performance.


>Let me making sure I'm parsing this statement properly: are you launching 200 MPI processes on 2 computers?  If so, do >those computers each have 100 cores?


>I ask because oversubscribing MPI processes (i.e., putting more than 1 process per core) will be disastrous to >performance.


>> I have measured each operation time and I haver realised that the MPI_Gather operation takes about 1 second in each >>synchronization (only an integer is send in each case). Is this time range normal or I have a synchronization >>problem?  Is there any way to improve this performance?


>I'm afraid I can't say more without more information about your hardware and software setup.  Is this a dedicated HPC >cluster?  Are you oversubscribing the cores?  What kind of Ethernet switching gear do you have?  ...etc.



>Jeff Squyres


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