The OpenMP* execution model has a single host device but multiple target devices. A device is a logical execution engine with its own local storage and data environment.

When executing on ATS or PVC, the entire GPU (which is composed of 2-tiles) can be considered as a device, or each tile can be considered as a device.

OpenMP starts executing on the host. When a host thread encounters a

target

construct, data is transferred from host to device (if specified by

map

clauses, for example), and code in the construct is offloaded onto the device. At the end of the

target

region, data is transferred from device to host (if so specified).

By default, the host thread waits for the

target

region to finish before proceeding further.

nowait

on a

target

construct specifies that the host thread does not need to wait for the

target

region to finish. In other words, the

nowait

clause allows the asynchronous execution of the

target

region.

Synchronizations between regions of the code executing asynchronously can be achieved via the

taskwait

directive,

depend

clauses, (implicit and explicit) barriers, or other synchronization mechanisms.