Chapel

Controlling number of threads

By default Chapel programs will use as many threads as the number of available physical cores. On Apple cpus, only the performance cores seems to be used by default. This can be by setting

export CHPL_RT_USE_PU_KIND=all # options: performance, efficiency, all

To control the number of threads, set the environment variables

export CHPL_RT_NUM_THREADS_PER_LOCALE=#

or specify it as an argument

./exe --dataParTasksPerLocale #

See the Chapel documentation for more on this.

Optimization flags --fast

With this flag enabled, many checks, like array bounds will not be performed during run time. So if you have bugs, they may be hard to find. If your code is not running correctly, always compile without this flag so that bugs can be found.