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CUDA.md

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CUDA GPUs

Mapping the abstraction to GPUs supporting CUDA is straightforward because the hierarchy levels are identical up to the element level. So blocks of warps of threads will be mapped directly to their CUDA equivalent.

The element level will be supported through an additional run-time variable containing the extent of elements per thread. This variable can be accessed by all threads and should optimally be placed in constant device memory for fast access.

Porting CUDA to alpaka

Nearly all CUDA functionality can be directly mapped to alpaka function calls. A major difference is that CUDA requires the block and grid sizes to be given in (x, y, z) order. Alpaka uses the mathematical C/C++ array indexing scheme [z][y][x]. Dimension 0 in this case is z, dimensions 2 is x.

Furthermore alpaka does not require the indices and extents to be 3-dimensional. The accelerators are templatized on and support arbitrary dimensionality. NOTE: Currently the CUDA implementation is restricted to a maximum of 3 dimensions!

NOTE: The CUDA-accelerator back-end can change the current CUDA device and will NOT set the device back to the one prior to the invocation of the alpaka function!

The following tables list the functions available in the CUDA Runtime API and their equivalent alpaka functions:

Device Management

CUDA alpaka
cudaChooseDevice -
cudaDeviceGetByPCIBusId -
cudaDeviceGetAttribute -
cudaDeviceGetCacheConfig -
cudaDeviceGetLimit -
cudaDeviceGetPCIBusId -
cudaDeviceGetSharedMemConfig -
cudaDeviceGetStreamPriorityRange -
cudaDeviceReset alpaka::dev::reset(device)
cudaDeviceSetCacheConfig -
cudaDeviceSetLimit -
cudaDeviceSetSharedMemConfig -
cudaDeviceSynchronize void alpaka::wait::wait(device)
cudaGetDevice n/a (no current device)
cudaGetDeviceCount std::size_t alpaka::dev::DevMan< TAcc >::getDeviceCount()
cudaGetDeviceProperties
  • alpaka::dev::DevProps alpaka::dev::getProps(device)
  • alpaka::acc::getAccDevProps(acc)
NOTE: Only some properties available
cudaIpcCloseMemHandle -
cudaIpcGetEventHandle -
cudaIpcGetMemHandle -
cudaIpcOpenEventHandle -
cudaIpcOpenMemHandle -
cudaSetDevice n/a (no current device)
cudaSetDeviceFlags -
cudaSetValidDevices -

Stream Management

CUDA alpaka
cudaStreamAddCallback -
cudaStreamAttachMemAsync -
cudaStreamCreate alpaka::stream::[StreamType] stream(device);
cudaStreamCreateWithFlags -
cudaStreamCreateWithPriority -
cudaStreamDestroy n/a (Destructor)
cudaStreamGetFlags -
cudaStreamGetPriority -
cudaStreamQuery bool alpaka::stream::test(stream)
cudaStreamSynchronize void alpaka::wait::wait(stream)
cudaStreamWaitEvent void alpaka::wait::wait(stream, event)

Event Management

CUDA alpaka
cudaEventCreate alpaka::event::Event< TAcc > event(device);
cudaEventCreateWithFlags -
cudaEventDestroy n/a (Destructor)
cudaEventElapsedTime -
cudaEventQuery bool alpaka::event::test(event)
cudaEventRecord void alpaka::stream::enqueue(stream, event)
cudaEventSynchronize void alpaka::wait::wait(event)

Memory Management

CUDA alpaka
cudaArrayGetInfo -
cudaFree n/a (automatic memory management with reference counted memory handles)
cudaFreeArray -
cudaFreeHost n/a
cudaFreeMipmappedArray -
cudaGetMipmappedArrayLevel -
cudaGetSymbolAddress -
cudaGetSymbolSize -
cudaHostAlloc n/a
cudaHostGetDevicePointer -
cudaHostGetFlags -
cudaHostRegister -
cudaHostUnregister -
cudaMalloc alpaka::mem::buf::alloc(device, extents1D)
cudaMalloc3D alpaka::mem::buf::alloc(device, extents3D)
cudaMalloc3DArray -
cudaMallocArray -
cudaMallocHost alpaka::mem::buf::alloc(device, extents) 1D, 2D, 3D suppoorted!
cudaMallocManaged TODO
cudaMallocMipmappedArray -
cudaMallocPitch alpaka::mem::alloc(device, extents2D)
cudaMemGetInfo
  • alpaka::dev::getMemBytes
  • alpaka::dev::getFreeMemBytes
    cudaMemcpy alpaka::mem::view::copy(memBufDst, memBufSrc, extents1D)
    cudaMemcpy2D alpaka::mem::view::copy(memBufDst, memBufSrc, extents2D)
    cudaMemcpy2DArrayToArray -
    cudaMemcpy2DAsync alpaka::mem::view::copy(memBufDst, memBufSrc, extents2D, stream)
    cudaMemcpy2DFromArray -
    cudaMemcpy2DFromArrayAsync -
    cudaMemcpy2DToArray -
    cudaMemcpy2DToArrayAsync -
    cudaMemcpy3D alpaka::mem::view::copy(memBufDst, memBufSrc, extents3D)
    cudaMemcpy3DAsync alpaka::mem::view::copy(memBufDst, memBufSrc, extents3D, stream)
    cudaMemcpy3DPeer alpaka::mem::view::copy(memBufDst, memBufSrc, extents3D)
    cudaMemcpy3DPeerAsync alpaka::mem::view::copy(memBufDst, memBufSrc, extents3D, stream)
    cudaMemcpyArrayToArray -
    cudaMemcpyAsync alpaka::mem::view::copy(memBufDst, memBufSrc, extents1D, stream)
    cudaMemcpyFromArray -
    cudaMemcpyFromArrayAsync -
    cudaMemcpyFromSymbol -
    cudaMemcpyFromSymbolAsync -
    cudaMemcpyPeer alpaka::mem::view::copy(memBufDst, memBufSrc, extents1D)
    cudaMemcpyPeerAsync alpaka::mem::view::copy(memBufDst, memBufSrc, extents1D, stream)
    cudaMemcpyToArray -
    cudaMemcpyToArrayAsync -
    cudaMemcpyToSymbol -
    cudaMemcpyToSymbolAsync -
    cudaMemset alpaka::mem::view::set(memBufDst, byte, extents1D)
    cudaMemset2D alpaka::mem::view::set(memBufDst, byte, extents2D)
    cudaMemset2DAsync alpaka::mem::view::set(memBufDst, byte, extents2D, stream)
    cudaMemset3D alpaka::mem::view::set(memBufDst, byte, extents3D)
    cudaMemset3DAsync alpaka::mem::view::set(memBufDst, byte, extents3D, stream)
    cudaMemsetAsync alpaka::mem::view::set(memBufDst, byte, extents1D, stream)
    make_cudaExtent -
    make_cudaPitchedPtr -

    Execution Control

    CUDA alpaka
    cudaConfigureCall
    • alpaka::stream::enqueue(stream, kernel, params...)
    • alpaka::kernel::BlockSharedExternMemSizeBytes< TKernel< TAcc > >::getBlockSharedExternMemSizeBytes<...>(...)
    cudaFuncGetAttributes -
    cudaFuncSetCacheConfig -
    cudaFuncSetSharedMemConfig -
    cudaLaunch alpaka::stream::enqueue(stream, kernel, params...)
    cudaSetDoubleForDevice n/a (alpaka assumes double support)
    cudaSetDoubleForHost n/a (alpaka assumes double support)
    cudaSetupArgument alpaka::stream::enqueue(stream, kernel, params...)

    Occupancy

    CUDA alpaka
    cudaOccupancyMaxActiveBlocksPerMultiprocessor -

    Unified Addressing

    CUDA alpaka
    cudaPointerGetAttributes alpaka::mem::view::getPtrDev(view, device)

    Peer Device Memory Access

    CUDA alpaka
    cudaDeviceCanAccessPeer -
    cudaDeviceDisablePeerAccess -
    cudaDeviceEnablePeerAccess -

    OpenGL, DirectX, VDPAU, Graphics Interoperability

    not available

    Texture/Surface Reference/Object Management

    not available

    Version Management

    not available