OpenACC library and environment variables

There are two environment variables associated with the OpenACC library that may be used to control the device type and device number: ACC_DEVICE_TYPE and ACC_DEVICE_NUM, respectively. These two environment variables can be used as an alternative to calling acc_set_device_num(). As seen in the second use case, the device type and device number were specified using acc_set_device_num(). If however, the aforementioned environment variables were set, then the call to acc_set_device_num() would not be required.

The use of the environment variables is only relevant when an OpenACC function is called prior to a call to cudaCreate(). If cudaCreate() is called prior to a call to an OpenACC function, then you must call acc_set_device_num() [1].

[1]

More complete information about ACC_DEVICE_TYPE and ACC_DEVICE_NUM can be found in sections 4.1 and 4.2 of the OpenACC Application Programming Interface”, Version 2.6.