OpenCL Interoperability

API Reference

Overview

oneDNN uses the OpenCL runtime for GPU engines to interact with the GPU. Users may need to use oneDNN with other code that uses OpenCL. For that purpose, the library provides API extensions to interoperate with underlying OpenCL objects. This interoperability API is defined in the dnnl_ocl.hpp header.

The interoperability API is provided for two scenarios:

  • Construction of oneDNN objects based on existing OpenCL objects

  • Accessing OpenCL objects for existing oneDNN objects

The mapping between oneDNN and OpenCL objects is provided in the following table:

oneDNN object

OpenCL object(s)

Engine

cl_device_id and cl_context

Stream

cl_command_queue

Memory (Buffer-based)

cl_mem

Memory (USM-based)

Unified Shared Memory (USM) pointer

The table below summarizes how to construct oneDNN objects based on OpenCL objects and how to query underlying OpenCL objects for existing oneDNN objects.

oneDNN object

API to construct oneDNN object

API to access OpenCL object(s)

Engine

dnnl::ocl_interop::make_engine(cl_device_id, cl_context)

dnnl::ocl_interop::get_device(const engine &) dnnl::ocl_interop::get_context(const engine &)

Stream

dnnl::ocl_interop::make_stream(const engine &, cl_command_queue)

dnnl::ocl_interop::get_command_queue(const stream &)

Memory (Buffer-based)

dnnl::memory(const memory::desc &, const engine &, cl_mem)

dnnl::ocl_interop::get_mem_object(const memory &)

Memory (USM-based)

dnnl::ocl_interop::make_memory(const memory::desc &, const engine &, ocl_interop::memory_kind, void *)

dnnl::memory::get_data_handle()

OpenCL Buffers and USM Interfaces for Memory Objects

The memory model in OpenCL is based on OpenCL buffers. Intel extension further extends the programming model with a Unified Shared Memory (USM) alternative, which provides the ability to allocate and use memory in a uniform way on host and OpenCL devices.

oneDNN supports both buffer and USM memory models. The buffer model is the default. The USM model requires using the interoperability API.

To construct a oneDNN memory object, use one of the following interfaces:

To identify whether a memory object is USM-based or buffer-based, dnnl::ocl_interop::get_memory_kind() query can be used.

Note

oneDNN follows retain/release OpenCL semantics when using OpenCL objects during construction. An OpenCL object is retained on construction and released on destruction. This ensures that the OpenCL object will not be destroyed while the oneDNN object stores a reference to it.

The access interfaces do not retain the OpenCL object. It is the user’s responsibility to retain the returned OpenCL object if necessary.

USM memory doesn’t support retain/release OpenCL semantics. When constructing a oneDNN memory object using a user-provided USM pointer oneDNN doesn’t own the provided memory. It’s user’s responsibility to manage its lifetime.