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### ROCm/HIP

HIP is part of the ROC (Radeon Open Compute) platform for parallel computing on AMD and NVIDIA GPUs. The application programming interface of HIP gives access to GPU's instruction set and computation resources (Execution of compute kernels).

##### Synchronization with ROCm/HIP streams

HIP operation such as compute kernels or memory transfer (between host and device) can be grouped/queued by HIP streams. are executed on the GPUs. Boost.Fiber enables a fiber to sleep (suspend) till a HIP 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 HIP 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]{
        hipStream_t stream;
        hipStreamCreate( & stream);
        int size = 1024 * 1024;
        int full_size = 20 * size;
        int * host_a, * host_b, * host_c;
        hipHostMalloc( & host_a, full_size * sizeof( int), hipHostMallocDefault);
        hipHostMalloc( & host_b, full_size * sizeof( int), hipHostMallocDefault);
        hipHostMalloc( & host_c, full_size * sizeof( int), hipHostMallocDefault);
        int * dev_a, * dev_b, * dev_c;
        hipMalloc( & dev_a, size * sizeof( int) );
        hipMalloc( & dev_b, size * sizeof( int) );
        hipMalloc( & 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) {
            hipMemcpyAsync( dev_a, host_a + i, size * sizeof( int), hipMemcpyHostToDevice, stream);
            hipMemcpyAsync( dev_b, host_b + i, size * sizeof( int), hipMemcpyHostToDevice, stream);
            hipLaunchKernel(kernel, dim3(size / 256), dim3(256), 0, stream, size, dev_a, dev_b, dev_c);
            hipMemcpyAsync( host_c + i, dev_c, size * sizeof( int), hipMemcpyDeviceToHost, stream);
        }
        auto result = boost::fibers::hip::waitfor_all( stream); // suspend fiber till HIP stream has finished
        BOOST_ASSERT( stream == std::get< 0 >( result) );
        BOOST_ASSERT( hipSuccess == std::get< 1 >( result) );
        std::cout << "f1: GPU computation finished" << std::endl;
        hipHostFree( host_a);
        hipHostFree( host_b);
        hipHostFree( host_c);
        hipFree( dev_a);
        hipFree( dev_b);
        hipFree( dev_c);
        hipStreamDestroy( stream);
    });
    f.join();

##### Synopsis

    #include <boost/fiber/hip/waitfor.hpp>

    namespace boost {
    namespace fibers {
    namespace hip {

    std::tuple< hipStream_t, hipError_t > waitfor_all( hipStream_t st);
    std::vector< std::tuple< hipStream_t, hipError_t > > waitfor_all( hipStream_t ... st);

    }}}

##### Non-member function `hip::waitfor()`

    #include <boost/fiber/hip/waitfor.hpp>

    namespace boost {
    namespace fibers {
    namespace hip {

    std::tuple< hipStream_t, hipError_t > waitfor_all( hipStream_t st);
    std::vector< std::tuple< hipStream_t, hipError_t > > waitfor_all( hipStream_t ... st);

    }}}

Effects:

  Suspends active fiber till HIP stream has finished its operations.

Returns:

  tuple of stream reference and the HIP stream status