You can set the MPIR_PARAM_CH3_NO_LOCAL environment variable to 1. Refer to the README.envvar file. Antonio On Friday, September 13, 2013 08:53:36 AM Jiri Simsa wrote: Pavan, Thank you for your answer. That's precisely what I was looking for. Any chance there is a way to force the intranode communication to use tcp? --Jiri Within the node, it uses shared memory. Outside the node, it depends on the netmod you configured with. tcp is the default netmod. -- Pavan On Sep 12, 2013, at 2:24 PM, Jiri Simsa wrote:
The high-order bit of my question is: What OS interface(s) does MPICH use to transfer data from one MPI process to another?>>> On Thu, Sep 12, 2013 at 1:36 PM, Jiri Simsa <[email protected][1]> wrote:> Hello,>> I have been trying to understand how MPICH implements collective operations. To do so, I have been reading the MPICH source code and stepping through mpiexec executions.>> For the sake of this discussion, let's assume that all MPI processes are executed on the same computer using: mpiexec -n <n> <mpi_program>>> This is my current abstract understanding of MPICH:>> - mpiexec spawns a hydra_pmi_proxy process, which in turn spawns <n> instances of <mpi_program>> - hydra_pmi_proxy process uses socket pairs to communicate with the instances of <mpi_program>>> I am not quite sure though what happens under the hoods when a collective operation, such as MPI_Allreduce, is executed. I have noticed that instances of <mpi_program> create and listen on a socket in the course of executing MPI_Allreduce but I am not sure who connects to these sockets. Any chance someone could describe the data flow inside of MPICH when a collective operation, such as MPI_Allreduce, is executed? Thanks!>> Best,>> --Jiri Simsa>> _______________________________________________> discuss mailing list [email protected]
[2]> To manage subscription options or unsubscribe:> https://lists.mpich.org/mailman/listinfo/discuss[3] --Pavan Balaji http://www.mcs.anl.gov/~balaji[4] -------- [1] mailto:[email protected] [2] mailto:[email protected] [3] https://lists.mpich.org/mailman/listinfo/discuss [4] http://www.mcs.anl.gov/~balaji