simple_fft_block_fp16.cu

#include <iostream>
#include <vector>

#include <cuda_runtime_api.h>
#include <cufftdx.hpp>

#include "block_io.hpp"
#include "common.hpp"
#include "fp16_common.hpp"

template<class FFT, bool InputInRRIILayout = false, bool OutputInRRIILayout = false>
__launch_bounds__(FFT::max_threads_per_block) __global__ void block_fft_kernel(typename FFT::value_type* data) {
    using complex_type = typename FFT::value_type;

    // Local array for thread
    complex_type thread_data[FFT::storage_size];

    // ID of FFT in CUDA block, in range [0; FFT::ffts_per_block)
    const unsigned int local_fft_id = threadIdx.y;
    // Load data from global memory to registers
    example::io<FFT>::load<InputInRRIILayout>(data, thread_data, local_fft_id);

    // Execute FFT
    extern __shared__ complex_type shared_mem[];
    FFT().execute(thread_data, shared_mem);

    // Save results
    example::io<FFT>::store<OutputInRRIILayout>(thread_data, data, local_fft_id);
}

// In this example a one-dimensional complex-to-complex transform is performed by a CUDA block.
//
// One block is run, and it calculates four 128-point C2C half precision FFTs.
// Data is generated on host, copied to device buffer, and then results are copied back to host.
//
// Here, we're using complex<half2> with ((Real, Imag), (Real, Imag)) layout as the type of the input/output
// data passed to kernel, and later on the device layout is changed into RRII when values are being loaded.
template<unsigned int Arch>
void simple_block_fft_complex_half2() {
    using namespace cufftdx;

    // FFT is defined, its: size, type, direction, precision. Block() operator informs that FFT
    // will be executed on block level. Shared memory is required for co-operation between threads.
    // Additionally,
    using FFT          = decltype(Block() + Size<128>() + Type<fft_type::c2c>() + Direction<fft_direction::forward>() +
                         Precision<__half>() + ElementsPerThread<8>() + FFTsPerBlock<4>() + SM<Arch>());
    using complex_type = typename FFT::value_type;

    // Allocate managed memory for input/output
    complex_type* data;
    // For performance reasons half precision cuFFTDx FFTs has an implicit batching of 2 FFTs. This means that:
    // * Used complex type is complex<__half2>, and real type is __half2.
    // * Every thread processes values from two batches simultaneously using __half2 as the base type.
    // * Number of FFTs per block must be a multiple of 2.
    // * Complex data is processed in ((Real1, Real2), (Imag1, Imag2)) layout, where (Real1, Imag1) is a value from
    //   one batch, and (Real2, Imag2) is from a different batch.
    // * Real data is process using __half2 in (Real1, Real2) layout, where Real1 is a value from one batch, and
    //   Real2 is from a different batch.
    constexpr size_t implicit_batching = FFT::implicit_type_batching;
    auto             size              = FFT::ffts_per_block / implicit_batching * cufftdx::size_of<FFT>::value;
    auto             size_bytes        = size * sizeof(complex_type);
    CUDA_CHECK_AND_EXIT(cudaMallocManaged(&data, size_bytes));
    for (size_t i = 0; i < size; i++) {
        float v1 = static_cast<float>(i);
        float v2 = static_cast<float>(i + size);
        // Populate input with complex<half2> values in ((Real, Imag), (Real, Imag)) layout
        data[i] = complex_type {__half2 {v1, -v1}, __half2 {v2, -v2}};
    }

    std::cout << "input [1st FFT]:\n";
    for (size_t i = 0; i < cufftdx::size_of<FFT>::value; i++) {
        std::cout << __half2float(data[i].x.x) << " " << __half2float(data[i].x.y) << std::endl;
    }

    // Increase max shared memory if needed
    CUDA_CHECK_AND_EXIT(cudaFuncSetAttribute(
        block_fft_kernel<FFT>,
        cudaFuncAttributeMaxDynamicSharedMemorySize,
        FFT::shared_memory_size));

    // Invokes kernel with FFT::block_dim threads in CUDA block
    block_fft_kernel<FFT><<<1, FFT::block_dim, FFT::shared_memory_size>>>(data);
    CUDA_CHECK_AND_EXIT(cudaPeekAtLastError());
    CUDA_CHECK_AND_EXIT(cudaDeviceSynchronize());

    std::cout << "output [1st FFT]:\n";
    for (size_t i = 0; i < cufftdx::size_of<FFT>::value; i++) {
        std::cout << __half2float(data[i].x.x) << " " << __half2float(data[i].x.y) << std::endl;
    }

    CUDA_CHECK_AND_EXIT(cudaFree(data));
    std::cout << "Success" << std::endl;
}

template<unsigned int Arch>
struct simple_block_fft_complex_half2_functor {
    void operator()() { return simple_block_fft_complex_half2<Arch>(); }
};

int main(int, char**) {
    return example::sm_runner<simple_block_fft_complex_half2_functor>();
}