Execution Policies

Top Level Execution Policies

ExecutionPolicyConcept is the fundamental abstraction to represent “how” the execution of a Kokkos parallel pattern takes place.

Policy	Description
RangePolicy	Each iterate is an integer in a contiguous range
MDRangePolicy	Each iterate for each rank is an integer in a contiguous range
TeamPolicy	Assigns to each iterate in a contiguous range a team of threads

Nested Execution Policies

Nested Execution Policies are used to dispatch parallel work inside of an already executing parallel region either dispatched with a TeamPolicy or a task policy. NestedPolicies summary.

Policy	Description
TeamThreadMDRange	Used inside of a TeamPolicy kernel to perform nested parallel loops over a multidimensional range split over threads of a team.
TeamThreadRange	Used inside of a TeamPolicy kernel to perform nested parallel loops split over threads of a team.
TeamVectorMDRange	Used inside of a TeamPolicy kernel to perform nested parallel loops over a multidimensional range split over threads of a team and their vector lanes.
TeamVectorRange	Used inside of a TeamPolicy kernel to perform nested parallel loops split over threads of a team and their vector lanes.
ThreadVectorMDRange	Used inside of a TeamPolicy kernel to perform nested parallel loops over a multidimensional range with vector lanes of a thread.
ThreadVectorRange	Used inside of a TeamPolicy kernel to perform nested parallel loops with vector lanes of a thread.

Common Arguments for all Execution Policies

Execution Policies generally accept compile time arguments via template parameters and runtime parameters via constructor arguments or setter functions.

Tip

Template arguments can be given in arbitrary order.

Argument	Options	Purpose
ExecutionSpace	Serial, OpenMP, Threads, Cuda, HIP, SYCL, HPX	Specify the Execution Space to execute the kernel in. Defaults to Kokkos::DefaultExecutionSpace
Schedule	Schedule<Dynamic>, Schedule<Static>	Specify scheduling policy for work items. Dynamic scheduling is implemented through a work stealing queue. Default is machine and backend specific.
IndexType	e.g. IndexType<int>	Specify integer type to be used for traversing the iteration space. Defaults to the size_type of ExecutionSpaceConcept. Can affect the performance depending on the backend.
LaunchBounds	LaunchBounds<MaxThreads, MinBlocks>	Specifies hints to to the compiler about CUDA/HIP launch bounds.
WorkTag	SomeClass	Specify the work tag type used to call the functor operator. Any arbitrary type defaults to void.