This document is meant to be a guide on how to add a new BLAS Level 3 operation to portBLAS. It is mostly based on the work done when adding the TRSM algorithm to portBLAS.
The steps described here are just a guideline and may vary when doing the actual implementation.
The folder include/interface contains the public interface of portBLAS.
The files in this folder contain the functions that users can call to
run the available blas operations.
This folder has one file for each level of blas. For example, the trsm
function will be located in include/interface/blas3_interface.h.
When defining a new level 3 operation, the first step is to define the
user-facing function, in this case blas::_trsm, and declare the
internal function that will be implemented inside portBLAS,
called blas::internal::_trsm, similar to the following:
namespace blas {
namespace internal {
// Internal function that will be implemented in the portBLAS library
template <typename sb_handle_t, typename container_0_t, typename container_1_t,
typename element_t, typename index_t>
typename sb_handle_t::event_t _trsm(sb_handle_t& sb_handle, char Side,
char Triangle, char Transpose,
char Diagonal, index_t M,
index_t N, element_t alpha,
container_0_t A, index_t lda,
container_1_t B, index_t ldb);
}
// User-facing function to call the TRSM operation
template <typename sb_handle_t, typename container_0_t, typename container_1_t,
typename element_t, typename index_t>
typename sb_handle_t::event_t inline _trsm(
sb_handle_t& sb_handle, char Side, char Triangle, char Transpose, char Diagonal,
index_t M, index_t N, element_t alpha, container_0_t A, index_t lda,
container_1_t B, index_t ldb) {
return internal::_trsm(sb_handle, Side, Triangle, Transpose, Diagonal, M, N, alpha, A, lda,
B, ldb);
}
} // namespace internal
} // namespace blasDefining a test for the new function early on is the best way to proceed since it will allow adding new pieces of code in small batches. This can prevent several complex compilation issues when adding the actual implementation for the new operation.
Templated functions don't get instantiated until they are used somewhere, so the next step in adding a new operation is to define a test for it.
This can be done by adding a new file, corresponding to the new operation
in the folder test/blas3. Here we create the file test/blas3/blas3_trsm_test.cpp
with the following contents:
#include "blas_test.hpp"
// A list of parameters to be passed to the test. This type will be used to
// generate several combinations of input values for the function to be tested.
template <typename scalar_t>
using combination_t = std::tuple<int, int, char, char, char, char, scalar_t,
scalar_t, scalar_t, scalar_t>;
// Register the function that will run the test
template <typename scalar_t>
void run_test(const combination_t<scalar_t> combi) {
int m;
int n;
char transA;
char side;
char diag;
char triangle;
scalar_t alpha;
scalar_t ldaMul;
scalar_t ldbMul;
scalar_t unusedValue;
std::tie(m, n, transA, side, diag, triangle, alpha, ldaMul, ldbMul,
unusedValue) = combi;
//
// Perform any initialization here
//
// Create the SB_Handle for the test
auto q = make_queue();
SB_Handle sb_handle(q);
// Invoke the newly added operation
_trsm(sb_handle, side, triangle, transA, diag, m, n, alpha, a_gpu, lda, b_gpu, ldb);
// Verify the results
}
// Create the combinations of parameters to invoke the test
const auto combi = ::testing::Combine(::testing::Values(7, 513, 1027), // m
::testing::Values(7, 513, 1027), // n
::testing::Values('n', 't'), // transA
::testing::Values('l', 'r'), // side
::testing::Values('u', 'n'), // diag
::testing::Values('l', 'u'), // triangle
::testing::Values(1.0, 2.0), // alpha
::testing::Values(1.0, 2.0), // lda_mul
::testing::Values(1.0, 2.0), // ldb_mul
::testing::Values(0.0, NaN) // unused
);
// Finaly register the new test
BLAS_REGISTER_TEST_ALL(Trsm, combination_t, combi);By this point, you are expected to get a linker error saying the symbol for the internal
version of blas::internal::_trsm is undefined, and that is expected since we didn't
provide the internal implementation for the newly added _trsm function.
The next step is to provide the implementation of blas::internal::_trsm and instantiate
it somewhere.
We start by creating the internal file src/interface/trsm_interface.hpp. This file
will contain the actual implementation of _trsm, but note that the function is not
yet being instantiated so the linker error will persist at this point:
namespace blas {
namespace internal {
template <typename sb_handle_t, typename container_0_t, typename container_1_t,
typename element_t, typename index_t>
typename sb_handle_t::event_t _trsm(
sb_handle_t& sb_handle, char Side, char Triangle, char Transpose, char Diagonal,
index_t M, index_t N, element_t alpha, container_0_t A, index_t lda,
container_1_t B, index_t ldb) {
// Implementation of the new operation
// This will probably invoke a kernel which we don't yet have defined.
// This function can access any other operation defined in this
// or lower levels of blas. For example, one may want to invoke a gemm
// operation like the following
auto gemmEvent = internal::_gemm(
sb_handle, 'n', isTranspose ? 't' : 'n', M, currentBlockSize,
currentBlockSize, (i == 0) ? alpha : element_t{1}, B + i * ldb, ldb,
invA + i * blockSize, blockSize, element_t{0}, X + i * ldx, ldx);
trsmEvents = concatenate_vectors(trsmEvents, gemmEvent);
// Ultimately, a list of all events created in this function is returned
// to the user that can be used to wait on all or part of the internal
// operations required to perform the full computation
return trsmEvents;
}
} // namespace internal
} // namespace blasThe next step is to define the _trsm function in a .cpp file. In this way, when the client
binary is linked against portBLAS, the linker will find the definition of the missing symbol.
To do this, we create the source file that will contain instantiations of the new _trsm operation.
The file is located at src/interface/blas3/trsm.cpp.in. This is not the file that will be
compiled, but a template file that the python script python_generator/py_gen_blas_binary.py
will use to generate the actual source file where the instantiation of _trsm will happen.
The file src/interface/blas3/trsm.cpp.in must include all files that are necessary to successfully
compile blas::internal::_trsm, for this particular example, this file looks like the following:
#include "container/sycl_iterator.hpp"
#include "sb_handle/portblas_handle.hpp"
#include "sb_handle/kernel_constructor.hpp"
#include "operations/blas_constants.hpp"
#include "views/view_sycl.hpp"
#include "portblas_helper.h"
#include "interface/blas1_interface.hpp"
#include "interface/trsm_interface.hpp"
#include "operations/blas3/trsm.hpp"
namespace blas {
namespace internal {
template typename SB_Handle::event_t _trsm(
SB_Handle sb_handle, char Side, char Triangle, char Transpose, char Diagonal,
${INDEX_TYPE} M, ${INDEX_TYPE} N, ${DATA_TYPE} alpha,
BufferIterator<${DATA_TYPE}> A, ${INDEX_TYPE} lda,
BufferIterator<${DATA_TYPE}> B, ${INDEX_TYPE} ldb);
} // namespace internal
} // namespace blasWhere ${INDEX_TYPE} and ${DATA_TYPE} are going to be replaced by the appropriate types required to explicitly instantiate the new function Finally, the file src/interface/blas3/CMakeLists.txtmust be changed in order to generate instantiations of_trsm`.
The following entry must be added:
generate_blas_objects(blas3 trsm)After this, the new object file created must be added to the library and is done by adding a new
entry to cmake/CmakeFunctionHelper.cmake. At the end of this file there is a list of all object
files that are archived to form the portBLAS library. A new entry must be added in the function
build_library:
function (build_library LIB_NAME)
add_library(${LIB_NAME}
#
# Other objects here
#
$<TARGET_OBJECTS:trsm> # Add the new object here
)
endfunction(build_library)After this step the test defined for the new function will compile and link successfully and
blas::internal::_trsm will be called from the test.
So far we have looked at how to add a new public facing function and how to instantiate it internally so that the linker can find it when compiling user code. If the new operation can be implemented in terms of pre-existing operations, the job would be done, however, it is often the case that a new operation requires a new kernel to be implemented in order to perform some computation.
In the case of _trsm, we need to implement the diagonal blocks inversion algorithm using SYCL.
To add a new kernel we need to add the corresponding expression tree in the file include/operations/blas3_trees.h.
In the case of _trsm, we add a new struct called DiagonalBlocksInverter with the following interface:
namespace blas {
template <bool UnitDiag, bool Upper, int BlockSize, typename matrix_t>
struct DiagonalBlocksInverter {
using index_t = typename std::make_signed<typename matrix_t::index_t>::type;
using value_t = typename std::remove_cv<typename matrix_t::value_t>::type;
static constexpr index_t internalBlockSize = BlockSize;
static constexpr index_t outterBlockSize = BlockSize;
matrix_t A_;
matrix_t invA_;
index_t lda_;
index_t N_;
DiagonalBlocksInverter(matrix_t& A, matrix_t& invA);
bool valid_thread(cl::sycl::nd_item<1> id) const;
void bind(cl::sycl::handler& cgh);
void adjust_access_displacement();
template <typename local_memory_t>
void eval(local_memory_t localMem, cl::sycl::nd_item<1> id) noexcept;
};
template <bool UnitDiag, bool Upper, int BlockSize, typename matrix_t>
DiagonalBlocksInverter<UnitDiag, Upper, BlockSize, matrix_t>
make_diag_blocks_inverter(matrix_t& A, matrix_t& invA) {
return DiagonalBlocksInverter<UnitDiag, Upper, BlockSize, matrix_t>(A, invA);
}
}The make_diag_blocks_inverter is a utility function that will be used in blas::internal::_trsm
to instantiate the kernel. With this new interface defined, we can implement it internally by creating
a new file called src/operations/blas3/trsm.hpp. This file will contain the implementation
of DiagonalBlocksInverter and make_diag_blocks_inverter. The actual kernel is implemented
in DiagonalBlocksInverter::eval in this file.
The last part is to add this file in the include list in src/operations/blas3/blas3_trees.hpp.
portBLAS implements the netlib-blas interface, so there will be a system blas version of the operation
being added. In the case of _trsm, the
netlib-blas version of the function
can be called to verify that our implementation produces the correct results for a certain combination of parameters.
portBLAS provides a utility header that is used to invoke different system-blas functions for testing and benchmarking purposes.
To make the new operation available, add it to the file include/utils/system_reference_blas.hpp, like the following:
namespace reference_blas {
template <typename scalar_t>
void trsm(const char* side, const char* triangle, const char* transA,
const char *diag, int m, int n, scalar_t alpha, scalar_t A[], int lda,
scalar_t B[], int ldb) {
auto func = blas_system_function<scalar_t>(&cblas_strsm, &cblas_dtrsm);
func(CblasColMajor, c_side(*side), c_uplo(*triangle), c_trans(*transA),
c_diag(*diag), m, n, alpha, A, lda, B, ldb);
}
} // namespace reference_blasIn this way, this function can be used in tests or benchmarks:
reference_blas::trsm(&side, &triangle, &transA, &diag, m, n,
static_cast<data_t>(alpha), A.data(), lda, cpu_B.data(),
ldb);So results from the reference implementation can be used to check if the operation implemented is correct.
By following the steps described in this document, you can add a new operation in portBLAS alongside the tests required to validate the implementation.