Integrating a Third-Party Library to oneAPI Math Kernel Library (oneMKL) Interfaces

This step-by-step tutorial provides examples for enabling new third-party libraries in oneMKL.

oneMKL has a header-based implementation of the interface layer (include directory) and a source-based implementation of the backend layer for each third-party library (src directory). To enable a third-party library, you must update both parts of oneMKL and integrate the new third-party library to the oneMKL build and test systems.

For the new backend library and header naming please use the following template:

onemkl_<domain>_<3rd-party library short name>[<wrapper for specific target>]

Where <wrapper for specific target> is required only if multiple wrappers are provided from the same 3rd-party library, e.g., wrappers with Intel oneMKL C API for CPU target onemkl_blas_mklcpu.so and wrappers with Intel oneMKL DPC++ API for GPU target onemkl_blas_mklgpu.so.

If there is no need for multiple wrappers only <domain> and <3rd-party library short name> are required, e.g. onemkl_rng_curand.so

1. Create Header Files

2. Integrate Header Files

3. Create Wrappers

4. Integrate Wrappers To the Build System

5. Update the Test System

1. Create Header Files

For each new backend library, you should create the following two header files:

Header file with a declaration of entry points to the new third-party library wrappers
Compiler-time dispatching interface (see oneMKL Usage Models) for new third-party libraries

Header File Example: command to generate the header file with a declaration of BLAS entry points in the oneapi::mkl::newlib namespace

python scripts/generate_backend_api.py include/oneapi/mkl/blas.hpp \                                  # Base header file
                                       include/oneapi/mkl/blas/detail/newlib/onemkl_blas_newlib.hpp \ # Output header file
                                       oneapi::mkl::newlib                                            # Wrappers namespace

Code snippet of the generated header file include/oneapi/mkl/blas/detail/newlib/onemkl_blas_newlib.hpp

namespace oneapi {
namespace mkl {
namespace newlib {

void asum(sycl::queue &queue, std::int64_t n, sycl::buffer<float, 1> &x, std::int64_t incx,
          sycl::buffer<float, 1> &result);

Compile-time Dispatching Interface Example: command to generate the compile-time dispatching interface template instantiations for newlib and supported device newdevice

python scripts/generate_ct_instant.py   include/oneapi/mkl/blas/detail/blas_ct_templates.hpp \         # Base header file
                                        include/oneapi/mkl/blas/detail/newlib/blas_ct.hpp \            # Output header file
                                        include/oneapi/mkl/blas/detail/newlib/onemkl_blas_newlib.hpp \ # Header file with declaration of entry points to wrappers
                                        newlib \                                                       # Library name
                                        newdevice \                                                    # Backend name
                                        oneapi::mkl::newlib                                            # Wrappers namespace

Code snippet of the generated header file include/oneapi/mkl/blas/detail/newlib/blas_ct.hpp

namespace oneapi {
namespace mkl {
namespace blas {

template <>
void asum<library::newlib, backend::newdevice>(sycl::queue &queue, std::int64_t n,
                                               sycl::buffer<float, 1> &x, std::int64_t incx,
                                               sycl::buffer<float, 1> &result) {
    asum_precondition(queue, n, x, incx, result);
    oneapi::mkl::newlib::asum(queue, n, x, incx, result);
    asum_postcondition(queue, n, x, incx, result);
}

2. Integrate Header Files

Below you can see structure of oneMKL top-level include directory:

include/
    oneapi/
        mkl/
            mkl.hpp -> oneMKL spec APIs
            types.hpp  -> oneMKL spec types
            blas.hpp   -> oneMKL BLAS APIs w/ pre-check/dispatching/post-check
            detail/    -> implementation specific header files
                exceptions.hpp        -> oneMKL exception classes
                backends.hpp          -> list of oneMKL backends
                backends_table.hpp    -> table of backend libraries for each domain and device
                get_device_id.hpp     -> function to query device information from queue for Run-time dispatching
            blas/
                predicates.hpp -> oneMKL BLAS pre-check post-check
                detail/        -> BLAS domain specific implementation details
                    blas_loader.hpp       -> oneMKL Run-time BLAS API
                    blas_ct_templates.hpp -> oneMKL Compile-time BLAS API general templates
                    cublas/
                        blas_ct.hpp            -> oneMKL Compile-time BLAS API template instantiations for <cublas>
                        onemkl_blas_cublas.hpp -> backend wrappers library API
                    mklcpu/
                        blas_ct.hpp            -> oneMKL Compile-time BLAS API template instantiations for <mklcpu>
                        onemkl_blas_mklcpu.hpp -> backend wrappers library API
                    <other backends>/
            <other domains>/

To integrate the new third-party library to a oneMKL header-based part, following files from this structure should be updated:

include/oneapi/mkl/detail/backends.hpp: add the new backend

Example: add the newbackend backend

   enum class backend { mklcpu,
+                       newbackend,

   static backendmap backend_map = { { backend::mklcpu, "mklcpu" },
+                                    { backend::newbackend, "newbackend" },

include/oneapi/mkl/detail/backends_table.hpp: add new backend library for supported domain(s) and device(s)

Example: enable newlib for blas domain and newdevice device

   enum class device : uint16_t { x86cpu,
                                  ...
+                                 newdevice
                                };

   static std::map<domain, std::map<device, std::vector<const char*>>> libraries = {
       { domain::blas,
         { { device::x86cpu,
             {
   #ifdef ONEMKL_ENABLE_MKLCPU_BACKEND
                 LIB_NAME("blas_mklcpu")
   #endif
              } },
+          { device::newdevice,
+            {
+  #ifdef ONEMKL_ENABLE_NEWLIB_BACKEND
+                 LIB_NAME("blas_newlib")
+  #endif
+             } },

include/oneapi/mkl/detail/get_device_id.hpp: add new device detection mechanism for Run-time dispatching

Example: enable newdevice if the queue is targeted for the Host

   inline oneapi::mkl::device get_device_id(sycl::queue &queue) {
       oneapi::mkl::device device_id;
+      if (queue.is_host())
+          device_id=device::newdevice;

include/oneapi/mkl/blas.hpp: include the generated header file for the compile-time dispatching interface (see oneMKL Usage Models)

Example: add include/oneapi/mkl/blas/detail/newlib/blas_ct.hpp generated at the 1. Create Header Files step
```
   #include "oneapi/mkl/blas/detail/mklcpu/blas_ct.hpp"
   #include "oneapi/mkl/blas/detail/mklgpu/blas_ct.hpp"
+  #include "oneapi/mkl/blas/detail/newlib/blas_ct.hpp"
```

The new files generated at the 1. Create Header Files step result in the following updated structure of the BLAS domain header files.

include/
    oneapi/
        mkl/
            blas.hpp -> oneMKL BLAS APIs w/ pre-check/dispatching/post-check
            blas/
                predicates.hpp -> oneMKL BLAS pre-check post-check
                detail/        -> BLAS domain specific implementation details
                    blas_loader.hpp       -> oneMKL Run-time BLAS API
                    blas_ct_templates.hpp -> oneMKL Compile-time BLAS API general templates
                    cublas/
                        blas_ct.hpp            -> oneMKL Compile-time BLAS API template instantiations for <cublas>
                        onemkl_blas_cublas.hpp -> backend wrappers library API
                    mklcpu/
                        blas_ct.hpp            -> oneMKL Compile-time BLAS API template instantiations for <mklcpu>
                        onemkl_blas_mklcpu.hpp -> backend wrappers library API
    +              newlib/
    +                  blas_ct.hpp            -> oneMKL Compile-time BLAS API template instantiations for <newbackend>
    +                  onemkl_blas_newlib.hpp -> backend wrappers library API
                    <other backends>/
            <other domains>/

3. Create Wrappers

Wrappers convert Data Parallel C++ (DPC++) input data types to third-party library data types and call corresponding implementation from the third-party library. Wrappers for each third-party library are built to separate oneMKL backend libraries. The libonemkl.so dispatcher library loads the wrappers at run-time if you are using the interface for run-time dispatching, or you will link with them directly in case you are using the interface for compile-time dispatching (for more information see oneMKL Usage Models).

All wrappers and dispatcher library implementations are in the src directory:

src/
    include/
        function_table_initializer.hpp -> general loader implementation w/ global libraries table
    blas/
        function_table.hpp -> loaded BLAS functions declaration
        blas_loader.cpp -> BLAS wrappers for loader
        backends/
            cublas/ -> cuBLAS wrappers
            mklcpu/ -> Intel oneMKL CPU wrappers
            mklgpu/ -> Intel oneMKL GPU wrappers
            <other backend libraries>/
    <other domains>/

Each backend library should contain a table of all functions from the chosen domain.

scripts/generate_wrappers.py can help to generate wrappers with the "Not implemented" exception for all functions based on the provided header file.

You can modify wrappers generated with this script to enable third-party library functionality.

Example: generate wrappers for newlib based on the header files generated and integrated previously, and enable only one asum function

The command below generates two new files:

src/blas/backends/newlib/newlib_wrappers.cpp - DPC++ wrappers for all functions from include/oneapi/mkl/blas/detail/newlib/onemkl_blas_newlib.hpp
src/blas/backends/newlib/newlib_wrappers_table_dyn.cpp - structure of symbols for run-time dispatcher (in the same location as wrappers), suffix _dyn indicates that this file is required for dynamic library only.

python scripts/generate_wrappers.py include/oneapi/mkl/blas/detail/newlib/onemkl_blas_newlib.hpp \ # Base header file
                                    src/blas/function_table.hpp \                                  # Declaration for structure of symbols
                                    src/blas/backends/newlib/newlib_wrappers.cpp \                 # Output wrappers
                                    newlib                                                         # Library name

You can then modify src/blas/backends/newlib/newlib_wrappers.cpp to enable the C function newlib_sasum from the third-party library libnewlib.so.

To enable this function:

Include the header file newlib.h with the newlib_sasum function declaration
Convert all DPC++ parameters to proper C types: use the get_access method for input and output DPC++ buffers to get row pointers
Submit the DPC++ kernel with a C function call to newlib as single_task

The following code snippet is updated for src/blas/backends/newlib/newlib_wrappers.cpp:

    #if __has_include(<sycl/sycl.hpp>)
    #include <sycl/sycl.hpp>
    #else
    #include <CL/sycl.hpp>
    #endif

    #include "oneapi/mkl/types.hpp"

    #include "oneapi/mkl/blas/detail/newlib/onemkl_blas_newlib.hpp"
+
+    #include "newlib.h"

    namespace oneapi {
    namespace mkl {
    namespace newlib {

    void asum(sycl::queue &queue, std::int64_t n, sycl::buffer<float, 1> &x, std::int64_t incx,
               sycl::buffer<float, 1> &result) {
-       throw std::runtime_error("Not implemented for newlib");
+       queue.submit([&](sycl::handler &cgh) {
+           auto accessor_x      = x.get_access<sycl::access::mode::read>(cgh);
+           auto accessor_result = result.get_access<sycl::access::mode::write>(cgh);
+           cgh.single_task<class newlib_sasum>([=]() {
+               accessor_result[0] = ::newlib_sasum((const int)n, accessor_x.get_pointer(), (const int)incx);
+           });
+       });
    }

    void asum(sycl::queue &queue, std::int64_t n, sycl::buffer<double, 1> &x, std::int64_t incx,
              sycl::buffer<double, 1> &result) {
        throw std::runtime_error("Not implemented for newlib");
    }

Updated structure of the src folder with the newlib wrappers:

src/
    blas/
        loader.hpp -> general loader implementation w/ global libraries table
        function_table.hpp -> loaded BLAS functions declaration
        blas_loader.cpp -> BLAS wrappers for loader
        backends/
            cublas/ -> cuBLAS wrappers
            mklcpu/ -> Intel oneMKL CPU wrappers
            mklgpu/ -> Intel oneMKL GPU wrappers
 +          newlib/
 +              newlib.h
 +              newlib_wrappers.cpp
 +              newlib_wrappers_table_dyn.cpp
            <other backend libraries>/
    <other domains>/

4. Integrate Wrappers to the Build System

Here is the list of files that should be created/updated to integrate the new wrappers for the third-party library to the oneMKL build system:

Add the new option ENABLE_XXX_BACKEND for the new third-party library to the top of the CMakeList.txt file.

Example: changes for newlib in the top of the CMakeList.txt file
```
    option(ENABLE_MKLCPU_BACKEND "" ON)
    option(ENABLE_MKLGPU_BACKEND "" ON)
+   option(ENABLE_NEWLIB_BACKEND "" ON)
```
Add the new directory (src/<domain>/backends/<new_directory>) with the wrappers for the new third-party library under the ENABLE_XXX_BACKEND condition to the src/<domain>/backends/CMakeList.txt file.

Example: changes for newlib in src/blas/backends/CMakeLists.txt
```
    if(ENABLE_MKLCPU_BACKEND)
        add_subdirectory(mklcpu)
    endif()
+
+   if(ENABLE_NEWLIB_BACKEND)
+       add_subdirectory(newlib)
+   endif()
```

Create the cmake/FindXXX.cmake cmake config file to find the new third-party library and its dependencies.

Example: new config file cmake/FindNEWLIB.cmake for newlib

include_guard()
# Find library by name in NEWLIB_ROOT cmake variable or environment variable NEWLIBROOT
find_library(NEWLIB_LIBRARY NAMES newlib
    HINTS ${NEWLIB_ROOT} $ENV{NEWLIBROOT}
    PATH_SUFFIXES "lib")
# Make sure that the library was found
include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(NEWLIB REQUIRED_VARS NEWLIB_LIBRARY)
# Set cmake target for the library
add_library(ONEMKL::NEWLIB::NEWLIB UNKNOWN IMPORTED)
set_target_properties(ONEMKL::NEWLIB::NEWLIB PROPERTIES
    IMPORTED_LOCATION ${NEWLIB_LIBRARY})

Create the src/<domain>/backends/<new_directory>/CMakeList.txt cmake config file to specify how to build the backend layer for the new third-party library.

scripts/generate_cmake.py can help to generate the initial src/<domain>/backends/<new_directory>/CMakeList.txt config file automatically for all files in the directory. Note: all source files with the _dyn suffix are added to build if the target is a dynamic library only.

Example: command to generate the cmake config file for the src/blas/backends/newlib directory
```
python scripts/generate_cmake.py src/blas/backends/newlib \ # Full path to the directory
                                 newlib                     # Library name
```
You should manually update the generated config file with information about the new cmake/FindXXX.cmake file and instructions about how to link with the third-party library.

Example: update the generated src/blas/backends/newlib/CMakeLists.txt file
```
    # Add third-party library
-   # find_package(XXX REQUIRED)
+   find_package(NEWLIB REQUIRED)
```
```
    target_link_libraries(${LIB_OBJ}
        PUBLIC ONEMKL::SYCL::SYCL
-       # Add third-party library to link with here
+       PUBLIC ONEMKL::NEWLIB::NEWLIB
    )
```

Now you can build the backend library for newlib to make sure the third-party library integration was completed successfully (for more information, see Build with cmake)

cd build/
cmake .. -DNEWLIB_ROOT=<path/to/newlib> \
    -DENABLE_MKLCPU_BACKEND=OFF \
    -DENABLE_MKLGPU_BACKEND=OFF \
    -DENABLE_NEWLIB_BACKEND=ON \           # Enable new third-party library backend
    -DBUILD_FUNCTIONAL_TESTS=OFF           # At this step we want build only
cmake --build . -j4

5. Update the Test System

Update the following files to enable the new third-party library for unit tests:

src/config.hpp.in: add a cmake option for the new third-party library so this macro can be propagated to unit tests

Example: add ENABLE_NEWLIB_BACKEND
```
   #cmakedefine ONEMKL_ENABLE_MKLCPU_BACKEND
+  #cmakedefine ONEMKL_ENABLE_NEWLIB_BACKEND
```

tests/unit_tests/CMakeLists.txt: add instructions about how to link tests with the new backend library

Example: add the newlib backend library

   if(ENABLE_MKLCPU_BACKEND)
       add_dependencies(test_main_ct onemkl_blas_mklcpu)
       if(BUILD_SHARED_LIBS)
           list(APPEND ONEMKL_LIBRARIES onemkl_blas_mklcpu)
       else()
           list(APPEND ONEMKL_LIBRARIES -foffload-static-lib=${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libonemkl_blas_mklcpu.a)
           find_package(MKL REQUIRED)
           list(APPEND ONEMKL_LIBRARIES ${MKL_LINK_C})
       endif()
   endif()
+
+    if(ENABLE_NEWLIB_BACKEND)
+       add_dependencies(test_main_ct onemkl_blas_newlib)
+       if(BUILD_SHARED_LIBS)
+           list(APPEND ONEMKL_LIBRARIES onemkl_blas_newlib)
+       else()
+           list(APPEND ONEMKL_LIBRARIES -foffload-static-lib=${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libonemkl_blas_newlib.a)
+           find_package(NEWLIB REQUIRED)
+           list(APPEND ONEMKL_LIBRARIES ONEMKL::NEWLIB::NEWLIB)
+       endif()
+   endif()

tests/unit_tests/include/test_helper.hpp: add the helper function for the compile-time dispatching interface with the new backend, and specify the device for which it should be called

Example: add the helper function for the newlib compile-time dispatching interface with newdevice if it is the Host

   #ifdef ONEMKL_ENABLE_MKLGPU_BACKEND
       #define TEST_RUN_INTELGPU(q, func, args) \
           func<oneapi::mkl::backend::mklgpu> args
   #else
       #define TEST_RUN_INTELGPU(q, func, args)
   #endif
+
+  #ifdef ONEMKL_ENABLE_NEWLIB_BACKEND
+     #define TEST_RUN_NEWDEVICE(q, func, args) \
+         func<oneapi::mkl::backend::newbackend> args
+  #else
+      #define TEST_RUN_NEWDEVICE(q, func, args)
+  #endif

   #define TEST_RUN_CT(q, func, args)               \
       do {                                         \
+          if (q.is_host())                         \
+              TEST_RUN_NEWDEVICE(q, func, args);   \

tests/unit_tests/main_test.cpp: add the targeted device to the vector of devices to test

Example: add the targeted device CPU for newlib

           }
       }
+
+  #ifdef ONEMKL_ENABLE_NEWLIB_BACKEND
+      devices.push_back(sycl::device(sycl::host_selector()));
+  #endif

Now you can build and run functional testing for enabled third-party libraries (for more information see Build with cmake).

cd build/
cmake .. -DNEWLIB_ROOT=<path/to/newlib> \
    -DENABLE_MKLCPU_BACKEND=OFF \
    -DENABLE_MKLGPU_BACKEND=OFF \
    -DENABLE_NEWLIB_BACKEND=ON  \
    -DBUILD_FUNCTIONAL_TESTS=ON
cmake --build . -j4
ctest

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create_new_backend.rst

Integrating a Third-Party Library to oneAPI Math Kernel Library (oneMKL) Interfaces

1. Create Header Files

2. Integrate Header Files

3. Create Wrappers

4. Integrate Wrappers to the Build System

5. Update the Test System

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Integrating a Third-Party Library to oneAPI Math Kernel Library (oneMKL) Interfaces

1. Create Header Files

2. Integrate Header Files

3. Create Wrappers

4. Integrate Wrappers to the Build System

5. Update the Test System