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- [/
- Copyright Oliver Kowalke 2017.
- Distributed under the Boost Software License, Version 1.0.
- (See accompanying file LICENSE_1_0.txt or copy at
- http://www.boost.org/LICENSE_1_0.txt
- ]
- [#cuda]
- [section:cuda CUDA]
- [@http://developer.nvidia.com/cuda-zone/ CUDA (Compute Unified Device Architecture)] is a platform for parallel computing
- on NVIDIA GPUs. The application programming interface of CUDA gives access to
- GPU's instruction set and computation resources (Execution of compute kernels).
- [heading Synchronization with CUDA streams]
- CUDA operation such as compute kernels or memory transfer (between host and
- device) can be grouped/queued by CUDA streams. are executed on the GPUs.
- Boost.Fiber enables a fiber to sleep (suspend) till a CUDA stream has completed
- its operations. This enables applications to run other fibers on the CPU without
- the need to spawn an additional OS-threads. And resume the fiber when the CUDA
- streams has finished.
- __global__
- void kernel( int size, int * a, int * b, int * c) {
- int idx = threadIdx.x + blockIdx.x * blockDim.x;
- if ( idx < size) {
- int idx1 = (idx + 1) % 256;
- int idx2 = (idx + 2) % 256;
- float as = (a[idx] + a[idx1] + a[idx2]) / 3.0f;
- float bs = (b[idx] + b[idx1] + b[idx2]) / 3.0f;
- c[idx] = (as + bs) / 2;
- }
- }
- boost::fibers::fiber f([&done]{
- cudaStream_t stream;
- cudaStreamCreate( & stream);
- int size = 1024 * 1024;
- int full_size = 20 * size;
- int * host_a, * host_b, * host_c;
- cudaHostAlloc( & host_a, full_size * sizeof( int), cudaHostAllocDefault);
- cudaHostAlloc( & host_b, full_size * sizeof( int), cudaHostAllocDefault);
- cudaHostAlloc( & host_c, full_size * sizeof( int), cudaHostAllocDefault);
- int * dev_a, * dev_b, * dev_c;
- cudaMalloc( & dev_a, size * sizeof( int) );
- cudaMalloc( & dev_b, size * sizeof( int) );
- cudaMalloc( & dev_c, size * sizeof( int) );
- std::minstd_rand generator;
- std::uniform_int_distribution<> distribution(1, 6);
- for ( int i = 0; i < full_size; ++i) {
- host_a[i] = distribution( generator);
- host_b[i] = distribution( generator);
- }
- for ( int i = 0; i < full_size; i += size) {
- cudaMemcpyAsync( dev_a, host_a + i, size * sizeof( int), cudaMemcpyHostToDevice, stream);
- cudaMemcpyAsync( dev_b, host_b + i, size * sizeof( int), cudaMemcpyHostToDevice, stream);
- kernel<<< size / 256, 256, 0, stream >>>( size, dev_a, dev_b, dev_c);
- cudaMemcpyAsync( host_c + i, dev_c, size * sizeof( int), cudaMemcpyDeviceToHost, stream);
- }
- auto result = boost::fibers::cuda::waitfor_all( stream); // suspend fiber till CUDA stream has finished
- BOOST_ASSERT( stream == std::get< 0 >( result) );
- BOOST_ASSERT( cudaSuccess == std::get< 1 >( result) );
- std::cout << "f1: GPU computation finished" << std::endl;
- cudaFreeHost( host_a);
- cudaFreeHost( host_b);
- cudaFreeHost( host_c);
- cudaFree( dev_a);
- cudaFree( dev_b);
- cudaFree( dev_c);
- cudaStreamDestroy( stream);
- });
- f.join();
- [heading Synopsis]
- #include <boost/fiber/cuda/waitfor.hpp>
- namespace boost {
- namespace fibers {
- namespace cuda {
- std::tuple< cudaStream_t, cudaError_t > waitfor_all( cudaStream_t st);
- std::vector< std::tuple< cudaStream_t, cudaError_t > > waitfor_all( cudaStream_t ... st);
- }}}
- [ns_function_heading cuda..waitfor]
- #include <boost/fiber/cuda/waitfor.hpp>
- namespace boost {
- namespace fibers {
- namespace cuda {
- std::tuple< cudaStream_t, cudaError_t > waitfor_all( cudaStream_t st);
- std::vector< std::tuple< cudaStream_t, cudaError_t > > waitfor_all( cudaStream_t ... st);
- }}}
- [variablelist
- [[Effects:] [Suspends active fiber till CUDA stream has finished its operations.]]
- [[Returns:] [tuple of stream reference and the CUDA stream status]]
- ]
- [endsect]
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