The HPCANDISC Procedure

Multithreading

Threading is the organization of computational work into multiple tasks (processing units that can be scheduled by the operating system). A task is associated with a thread. Multithreading is the concurrent execution of threads. When multithreading is possible, you can realize substantial performance gains compared to the performance that you get from sequential (single-threaded) execution.

The number of threads that the HPCANDISC procedure spawns is determined by the number of CPUs on a machine and can be controlled in the following ways:

  • You can specify the CPU count by using the CPUCOUNT= SAS system option. For example, if you specify the following statement, PROC HPCANDISC schedules threads as if it were executing on a system that had four CPUs, regardless of the actual CPU count: 

    options cpucount=4;

  • You can specify the NTHREADS= option in the PERFORMANCE statement to determine the number of threads. This specification overrides the system option. Specify NTHREADS=1 to force single-threaded execution.

The number of threads per machine is displayed in the "Performance Information" table, which is part of the default output. The HPCANDISC procedure allocates one thread per CPU.

The tasks that are multithreaded by the HPCANDISC procedure are primarily defined by dividing the data processed on a single machine among the threads; that is, PROC HPCANDISC implements multithreading through a data-parallel model. For example, if the input data set has 1,000 observations and you are running on four threads, then 250 observations are associated with each thread. All operations that require access to the data are then multithreaded. These operations include the following:

  • variable levelization

  • formation of the crossproducts matrix

  • canonical variable scoring of observations