[FFmpeg-devel] [PATCH] dxva: wait until D3D11 buffer copies are done before submitting them

[Steve Lhomme]

On 2020-08-05 9:07, Steve Lhomme wrote:
> When used aggressively, calling SubmitDecoderBuffers() just after
> ReleaseDecoderBuffer() may have the buffers not used properly and created

*creates

> decoding artifacts.
> It's likely due to the time to copy the submitted buffer in CPU mapped memory
> to GPU memory. SubmitDecoderBuffers() doesn't appear to wait for the state
> of the buffer submitted to become "ready".

I noticed this behaviour on a 48 threads machine. In VLC we use a lot of 
threads for lavc, even with D3D11. And the more threads I added, the 
more artifacts I got. Adding this code solved the issue. The decoder is 
now guaranteed to have all the buffers in the GPU when submitting them 
for decoding.

> For now it's not supported in the legacy API using AVD3D11VAContext, we need to
> add a ID3D11DeviceContext in there as it cannot be derived from the other
> interfaces we provide (ID3D11VideoContext is not a kind of ID3D11DeviceContext).
> ---
>   libavcodec/dxva2.c          | 32 ++++++++++++++++++++++++++++++++
>   libavcodec/dxva2_internal.h |  2 ++
>   2 files changed, 34 insertions(+)
> 
> diff --git a/libavcodec/dxva2.c b/libavcodec/dxva2.c
> index 32416112bf..dbbad8ed00 100644
> --- a/libavcodec/dxva2.c
> +++ b/libavcodec/dxva2.c
> @@ -692,6 +692,12 @@ int ff_dxva2_decode_init(AVCodecContext *avctx)
>           d3d11_ctx->surface       = sctx->d3d11_views;
>           d3d11_ctx->workaround    = sctx->workaround;
>           d3d11_ctx->context_mutex = INVALID_HANDLE_VALUE;
> +
> +        D3D11_QUERY_DESC query = { 0 };
> +        query.Query = D3D11_QUERY_EVENT;
> +        if (FAILED(ID3D11Device_CreateQuery(device_hwctx->device, &query,
> +                                            (ID3D11Query**)&sctx->wait_copies)))
> +            sctx->wait_copies = NULL;
>       }
>   #endif
>   
> @@ -729,6 +735,8 @@ int ff_dxva2_decode_uninit(AVCodecContext *avctx)
>       av_buffer_unref(&sctx->decoder_ref);
>   
>   #if CONFIG_D3D11VA
> +    if (sctx->wait_copies)
> +        ID3D11Asynchronous_Release(sctx->wait_copies);
>       for (i = 0; i < sctx->nb_d3d11_views; i++) {
>           if (sctx->d3d11_views[i])
>               ID3D11VideoDecoderOutputView_Release(sctx->d3d11_views[i]);
> @@ -932,6 +940,13 @@ int ff_dxva2_common_end_frame(AVCodecContext *avctx, AVFrame *frame,
>   
>   #if CONFIG_D3D11VA
>       if (ff_dxva2_is_d3d11(avctx)) {
> +        if (sctx->wait_copies)
> +        {
> +            AVHWFramesContext *frames_ctx = (AVHWFramesContext*)avctx->hw_frames_ctx->data;
> +            AVD3D11VADeviceContext *device_hwctx = frames_ctx->device_ctx->hwctx;
> +            ID3D11DeviceContext_Begin(device_hwctx->device_context, sctx->wait_copies);
> +        }
> +
>           buffer = &buffer11[buffer_count];
>           type = D3D11_VIDEO_DECODER_BUFFER_PICTURE_PARAMETERS;
>       }
> @@ -1005,9 +1020,26 @@ int ff_dxva2_common_end_frame(AVCodecContext *avctx, AVFrame *frame,
>   
>   #if CONFIG_D3D11VA
>       if (ff_dxva2_is_d3d11(avctx))
> +    {
> +        int maxWait = 10;
> +        /* wait until all the buffer release is done copying data to the GPU
> +         * before doing the submit command */
> +        if (sctx->wait_copies)
> +        {
> +            AVHWFramesContext *frames_ctx = (AVHWFramesContext*)avctx->hw_frames_ctx->data;
> +            AVD3D11VADeviceContext *device_hwctx = frames_ctx->device_ctx->hwctx;
> +            ID3D11DeviceContext_End(device_hwctx->device_context, sctx->wait_copies);
> +
> +            while (maxWait-- && S_FALSE ==
> +                   ID3D11DeviceContext_GetData(device_hwctx->device_context,
> +                                               sctx->wait_copies, NULL, 0, 0))
> +                SleepEx(2, TRUE);

And just as I submit this I realize it should be unlocking the device 
context while waiting.

> +        }
> +
>           hr = ID3D11VideoContext_SubmitDecoderBuffers(D3D11VA_CONTEXT(ctx)->video_context,
>                                                        D3D11VA_CONTEXT(ctx)->decoder,
>                                                        buffer_count, buffer11);
> +    }
>   #endif
>   #if CONFIG_DXVA2
>       if (avctx->pix_fmt == AV_PIX_FMT_DXVA2_VLD) {
> diff --git a/libavcodec/dxva2_internal.h b/libavcodec/dxva2_internal.h
> index b822af59cd..c44e8e09b0 100644
> --- a/libavcodec/dxva2_internal.h
> +++ b/libavcodec/dxva2_internal.h
> @@ -81,6 +81,8 @@ typedef struct FFDXVASharedContext {
>       ID3D11VideoDecoderOutputView  **d3d11_views;
>       int                          nb_d3d11_views;
>       ID3D11Texture2D                *d3d11_texture;
> +
> +    ID3D11Asynchronous             *wait_copies;
>   #endif
>   
>   #if CONFIG_DXVA2
> -- 
> 2.26.2
> 
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