Hello, We used to use mpich2-1.2 with gforker process manager (Intel 10.1 compiler). We are transitioning mpich-3.2 with gforker process manager (Intel 13.1 compiler) (configuration options are the same as before: ./configure --prefix=$MPI_DIR --enable-g=debug,meminit --enable-fast=O2 --with-pm=gforker --enable-cxx --enable-fortran CC=icc CXX=icpc FC=ifort F77=ifort) We have noticed extreme slowdowns with the new installation of mpich on the same machine (shared memory Linux server with CentOS 7) when attempting to use hyperthreading. The old executable works just fine on the same machine, but the new executable using mpich-3.2 is running 10-20x slower when going past the number of physical cores on the machine. We believe we have traced it to our MPI_AllReduce functions. This is a Fortran code. In the meantime I'm going to try to install the old mpich2-1.2 again (we had a machine OS upgrade) and see what happens. Any ideas? Thank you, Emily Shemon, Ph.D. Argonne National Laboratory Nuclear Engineering Division & Argonne Leadership Computing Facility P: 630-252-4477 E: [email protected]<mailto:[email protected]> _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss