Re: [OMPI users] difference between single and double precision

2010-12-20 Thread Mathieu Gontier
Hi, I am now ok with the env. var. Pretty simple to set and get into the code to pack the messages. About tests, it is so dependent on the cluster, OpenMPI itself and the model, this way is not an industrial way of tuning the computation. But the env. var. is a good workaround. Thanks again

[OMPI users] Running OpenMPI on SGI Altix with 4096 cores : very poor performance

2010-12-20 Thread Gilbert Grosdidier
Bonjour, I am now at a loss with my running of OpenMPI (namely 1.4.3) on a SGI Altix cluster with 2048 or 4096 cores, running over Infiniband. After fixing several rather obvious failures with Ralph, Jeff and John help, I am now facing the bottom of this story since : - there are no more

Re: [OMPI users] Running OpenMPI on SGI Altix with 4096 cores : very poor performance

2010-12-20 Thread George Bosilca
Are your processes places the same way with the two MPI implementations? Per-node vs. per-core ? george. On Dec 20, 2010, at 11:14 , Gilbert Grosdidier wrote: > Bonjour, > > I am now at a loss with my running of OpenMPI (namely 1.4.3) > on a SGI Altix cluster with 2048 or 4096 cores,

Re: [OMPI users] Running OpenMPI on SGI Altix with 4096 cores : very poor performance

2010-12-20 Thread Gilbert Grosdidier
Yes, there is definitely only 1 process per core with both MPI implementations. Thanks, G. Le 20/12/2010 20:39, George Bosilca a écrit : Are your processes places the same way with the two MPI implementations? Per-node vs. per-core ? george. On Dec 20, 2010, at 11:14 , Gilbert

Re: [OMPI users] Running OpenMPI on SGI Altix with 4096 cores : very poor performance

2010-12-20 Thread George Bosilca
That's a first step. My question was more related to the process overlay on the cores. If the MPI implementation place one process per node, then rank k and rank k+1 will always be on separate node, and the communications will have to go over IB. In the opposite if the MPI implementation places