I see a lot of functions, such as acc_get_num_devices(), requires as input the device type. I used int devtype=acc_get_device_type() that returns devtype=2.
(In the documenation: acc_get_num_devices( devicetype ) Returns the number of devices of the specified type)
What this 2 means? Which device types are there? Is device type an integer?
(Seems absurd to me I cannot find these info on the documentation)
Refer to section 2.4 of the specification for a general description of usage of
device_type. Also see Appendix A (not formally part of the specification) for recommendations for typical device types you might expect to encounter.The
device_typeis used to specify a particular accelerator type, and it is implementation defined. Therefore the specific types available for selection will be defined by the OpenACC aware compiler that you are using.Using the PGI compiler implementation, the choices for
device_typeshould correspond to the choices available for the-ta=...compiler switch.A typical use of a
device_typeclause on an OpenACC directive is to (further) condition the behavior of that directive for specific device types. For example, a specific optimization (such as choice of vector length to use) could be conditioned on running on a particulardevice_type.Here is a particular (obsolete) example. The device_type is used to either parallelize a particular loop, or run it sequentially, depending on device type that you are actually running on. I say obsolete because I don't think
-ta=radeonis a supported configuration for the most recent versions of the PGI OpenACC compilers (after 17.x). You can see another example of usage ofdevice_typein this blog and in this blogI believe in C/C++, the datatype is an enum type, whereas in Fortran it may formally be an integer. Naturally in C/C++, an enum may have an underlying integer association. Rather than worrying about the meaning of a specific integer value in a specific implementation, it's probably better to use the enums/defines to refer to these.