Exclusive Access to a Node's Processing and Memory Resources

Explains the aprun -F option.

The -F affinity option for aprun provides a program with exclusive access to all the processing and memory resources on a node.

This option assigns all compute node cores and compute node memory to the application's cpuset. Used with the -cc option, it enables an application programmer to bind processes to those mentioned in the affinity string.

There are two modes: exclusive and share. The share mode restricts the application specific cpuset contents to only the application reserved cores and memory on NUMA node boundaries. For example, if an application requests and is assigned cores and memory on NUMA node 0, then only NUMA node 0 cores and memory are contained within the application cpuset. The application cannot access the cores and memory of the other NUMA nodes on that compute node.

Administrators can modify /etc/opt/cray/alps/alps.conf to set a policy for access modes. If nodeShare is not specified in this file, the default mode remains exclusive; setting to share makes the default share access mode. Users can override the system-wide policy by specifying aprun -F exclusive at the command line or within their respective batch scripts. For additional information, see the aprun(1) man page.