[FFmpeg-devel] [PATCH] Allow using primary CUDA device context

[Oleg Dobkin]

I've changed enum into a flag and moved it into
AVCUDADeviceContextInternal.

> Can't one just call cuCtxGetDevice on the context to get the device?

Not sure the cuCtxGetDevice can be used for the primary context; also,
according to documentation it returns device id not handle. Anyway, is
it that bad to store an additional handle?

> Also needs configure updated for the higher ffnvcodec version

I'm looking at the configure and can't figure out how ffnvcodec version
is enforced. The script seems to accept several ranges of ffnvcodec
versions. I could just increment the top-level check, but I'm not sure
this is the correct way.

On Sun, 2019-11-17 at 23:31 +0100, Timo Rothenpieler wrote:
> On 17.11.2019 15:58, Oleg Dobkin wrote:
> 
> Add AVCUDADeviceContextFlags to control the creation of CUDA device
> context for the hardware CUDA decoder.
> 
> The current values are 0 (default behavior) - new context will be
> created for each decoder, and 1 - primary CUDA context will be used.
> 
> There are several reasons for using primary device context instead of
> creating a new one:
> 
>   - This is the recommended way to handle device contexts (see
> 
https://docs.nvidia.com/cuda/cuda-driver-api/group__CUDA__CTX.html#group__CUDA__CTX_1g65dc0012348bc84810e2103a40d8e2cf
> )
> 
>   - Memory allocations, kernels and other state are associated with
> the
> current device context. Currently, the context is not accessible from
> FFmpeg API, so, technically, the memory created by the hardware
> decoder
> (the video frame) can't be safely read.
> 
> Signed-off-by: Oleg Dobkin <olegd at anyvision.co>
> ---
>   libavutil/hwcontext_cuda.c | 20 +++++++++++++++-----
>   libavutil/hwcontext_cuda.h |  7 +++++++
>   2 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/libavutil/hwcontext_cuda.c b/libavutil/hwcontext_cuda.c
> index cca39e9fc7..608ea57569 100644
> --- a/libavutil/hwcontext_cuda.c
> +++ b/libavutil/hwcontext_cuda.c
> @@ -281,8 +281,12 @@ static void cuda_device_uninit(AVHWDeviceContext
> *device_ctx)
>       if (hwctx->internal) {
>           CudaFunctions *cu = hwctx->internal->cuda_dl;
>           if (hwctx->internal->is_allocated && hwctx->cuda_ctx) {
> -            CHECK_CU(cu->cuCtxDestroy(hwctx->cuda_ctx));
> +            if (hwctx->flags == DCF_CREATE_CONTEXT)
> 
> Should actually be checking for the flag, not equality.
> 
> 
> +                CHECK_CU(cu->cuCtxDestroy(hwctx->cuda_ctx));
> +            else
> +                CHECK_CU(cu->cuDevicePrimaryCtxRelease(hwctx-
> >cuda_device));
>               hwctx->cuda_ctx = NULL;
> +            hwctx->cuda_device = NULL;
>           }
>           cuda_free_functions(&hwctx->internal->cuda_dl);
>       }
> @@ -322,7 +326,6 @@ static int cuda_device_create(AVHWDeviceContext
> *device_ctx,
>   {
>       AVCUDADeviceContext *hwctx = device_ctx->hwctx;
>       CudaFunctions *cu;
> -    CUdevice cu_device;
>       CUcontext dummy;
>       int ret, device_idx = 0;
>   
> @@ -338,18 +341,25 @@ static int cuda_device_create(AVHWDeviceContext
> *device_ctx,
>       if (ret < 0)
>           goto error;
>   
> -    ret = CHECK_CU(cu->cuDeviceGet(&cu_device, device_idx));
> +    ret = CHECK_CU(cu->cuDeviceGet(&hwctx->cuda_device,
> device_idx));
>       if (ret < 0)
>           goto error;
>   
> -    ret = CHECK_CU(cu->cuCtxCreate(&hwctx->cuda_ctx,
> CU_CTX_SCHED_BLOCKING_SYNC, cu_device));
> +    hwctx->flags = flags;
> +
> +    if (flags == DCF_CREATE_CONTEXT)
> +        ret = CHECK_CU(cu->cuCtxCreate(&hwctx->cuda_ctx,
> CU_CTX_SCHED_BLOCKING_SYNC, hwctx->cuda_device));
> +    else
> +        ret = CHECK_CU(cu->cuDevicePrimaryCtxRetain(&hwctx-
> >cuda_ctx, hwctx->cuda_device));
> +
>       if (ret < 0)
>           goto error;
>   
>       // Setting stream to NULL will make functions automatically use
> the default CUstream
>       hwctx->stream = NULL;
>   
> -    CHECK_CU(cu->cuCtxPopCurrent(&dummy));
> +    if (flags == DCF_CREATE_CONTEXT)
> +        CHECK_CU(cu->cuCtxPopCurrent(&dummy));
>   
>       hwctx->internal->is_allocated = 1;
>   
> diff --git a/libavutil/hwcontext_cuda.h b/libavutil/hwcontext_cuda.h
> index 81a0552cab..bab5eefe54 100644
> --- a/libavutil/hwcontext_cuda.h
> +++ b/libavutil/hwcontext_cuda.h
> @@ -34,6 +34,11 @@
>    * AVBufferRefs whose data pointer is a CUdeviceptr.
>    */
>   
> +enum AVCUDADeviceContextFlags {
> +    DCF_CREATE_CONTEXT = 0,
> +    DCF_USE_PRIMARY_CONTEXT = 1
> +};
> 
> I'd only define a flag for the new behavior. If it's not set, keep
> old 
> behavior.
> 
> 
>   typedef struct AVCUDADeviceContextInternal
> AVCUDADeviceContextInternal;
>   
>   /**
> @@ -43,6 +48,8 @@ typedef struct AVCUDADeviceContext {
>       CUcontext cuda_ctx;
>       CUstream stream;
>       AVCUDADeviceContextInternal *internal;
> +    CUdevice cuda_device;
> 
> Can't one just call cuCtxGetDevice on the context to get the device?
> 
> 
> +    enum AVCUDADeviceContextFlags flags;
> 
> The device_create/av_hwdevice_ctx_create function already has a (at
> the 
> moment unused) flags parameter. So there should be no need to add
> this here.
> If need be, the information should be stored in 
> AVCUDADeviceContextInternal instead.
> 
> 
>   } AVCUDADeviceContext;
>   
> 
> Also needs configure updated for the higher ffnvcodec version that's 
> required after this patch, and probably deserved a lavu micro bump.
> 
> 
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