General Performance Tuning

MPI_POLLALL

When set to 1, the default value, all connections are polled for receives, also known as full polling. When set to 0, only those connections are polled where receives are posted. Full polling helps drain system buffers and so lessen the chance of deadlock for "unsafe" codes. Well-written codes should set MPI_POLLALL to 0 for best performance.

MPI_PROCBIND

Binds each MPI process to its own processor. By default, MPI_PROCBIND is set to 0, which means processor binding is off. To turn processor binding on, set it to 1. The system administrator may allow or disable processor binding by setting the pbind parameter in the hpc.conf file on or off. If this parameter is set, the MPI_PROCBIND environment variable is disabled. Performance can be enhanced with processor binding, but very poor performance will result if processor binding is used for multithreaded jobs or for more than one job at a time.

MPI_SPIN

Sets the spin policy. The default value is 0, which causes MPI processes to spin nonaggressively, allowing best performance when the load is at least as great as the number of CPUs. A value of 1 causes MPI processes to spin aggressively, leading to best performance if extra CPUs are available on each node to handle system daemons and other background activities.