[FFmpeg-devel] [PATCH 2/6] avcodec/nvdec: avoid needless copy of output frame

[Timo Rothenpieler]

Am 08.05.2018 um 17:25 schrieb wm4:
> On Tue,  8 May 2018 15:31:28 +0200
> Timo Rothenpieler <timo at rothenpieler.org> wrote:
> 
>> Replaces the data pointers with the mapped cuvid ones.
>> Adds buffer_refs to the frame to ensure the needed contexts stay alive
>> and the cuvid idx stays allocated.
>> Adds another buffer_ref to unmap the frame when it's unreferenced itself.
>> ---
>>   libavcodec/nvdec.c | 83 +++++++++++++++++++++++++++++++++-------------
>>   1 file changed, 60 insertions(+), 23 deletions(-)
>>
>> diff --git a/libavcodec/nvdec.c b/libavcodec/nvdec.c
>> index ab3cb88b27..d98f9dd95e 100644
>> --- a/libavcodec/nvdec.c
>> +++ b/libavcodec/nvdec.c
>> @@ -308,7 +308,7 @@ int ff_nvdec_decode_init(AVCodecContext *avctx)
>>       params.CodecType           = cuvid_codec_type;
>>       params.ChromaFormat        = cuvid_chroma_format;
>>       params.ulNumDecodeSurfaces = frames_ctx->initial_pool_size;
>> -    params.ulNumOutputSurfaces = 1;
>> +    params.ulNumOutputSurfaces = frames_ctx->initial_pool_size;
>>   
>>       ret = nvdec_decoder_create(&ctx->decoder_ref, frames_ctx->device_ref, &params, avctx);
>>       if (ret < 0) {
>> @@ -354,6 +354,32 @@ static void nvdec_fdd_priv_free(void *priv)
>>       av_freep(&priv);
>>   }
>>   
>> +static void nvdec_unmap_mapped_frame(void *opaque, uint8_t *data)
>> +{
>> +    NVDECFrame *unmap_data = (NVDECFrame*)data;
>> +    NVDECDecoder *decoder = (NVDECDecoder*)unmap_data->decoder_ref->data;
>> +    CUdeviceptr devptr = (CUdeviceptr)opaque;
>> +    CUresult err;
>> +    CUcontext dummy;
>> +
>> +    err = decoder->cudl->cuCtxPushCurrent(decoder->cuda_ctx);
>> +    if (err != CUDA_SUCCESS) {
>> +        av_log(NULL, AV_LOG_ERROR, "cuCtxPushCurrent failed\n");
>> +        goto finish;
>> +    }
>> +
>> +    err = decoder->cvdl->cuvidUnmapVideoFrame(decoder->decoder, devptr);
>> +    if (err != CUDA_SUCCESS)
>> +        av_log(NULL, AV_LOG_ERROR, "cuvidUnmapVideoFrame failed\n");
>> +
>> +    decoder->cudl->cuCtxPopCurrent(&dummy);
>> +
>> +finish:
>> +    av_buffer_unref(&unmap_data->idx_ref);
>> +    av_buffer_unref(&unmap_data->decoder_ref);
>> +    av_free(unmap_data);
>> +}
>> +
>>   static int nvdec_retrieve_data(void *logctx, AVFrame *frame)
>>   {
>>       FrameDecodeData  *fdd = (FrameDecodeData*)frame->private_ref->data;
>> @@ -361,6 +387,7 @@ static int nvdec_retrieve_data(void *logctx, AVFrame *frame)
>>       NVDECDecoder *decoder = (NVDECDecoder*)cf->decoder_ref->data;
>>   
>>       CUVIDPROCPARAMS vpp = { .progressive_frame = 1 };
>> +    NVDECFrame *unmap_data = NULL;
>>   
>>       CUresult err;
>>       CUcontext dummy;
>> @@ -383,32 +410,39 @@ static int nvdec_retrieve_data(void *logctx, AVFrame *frame)
>>           goto finish;
>>       }
>>   
>> -    for (i = 0; frame->data[i]; i++) {
>> -        CUDA_MEMCPY2D cpy = {
>> -            .srcMemoryType = CU_MEMORYTYPE_DEVICE,
>> -            .dstMemoryType = CU_MEMORYTYPE_DEVICE,
>> -            .srcDevice     = devptr,
>> -            .dstDevice     = (CUdeviceptr)frame->data[i],
>> -            .srcPitch      = pitch,
>> -            .dstPitch      = frame->linesize[i],
>> -            .srcY          = offset,
>> -            .WidthInBytes  = FFMIN(pitch, frame->linesize[i]),
>> -            .Height        = frame->height >> (i ? 1 : 0),
>> -        };
>> -
>> -        err = decoder->cudl->cuMemcpy2D(&cpy);
>> -        if (err != CUDA_SUCCESS) {
>> -            av_log(logctx, AV_LOG_ERROR, "Error copying decoded frame: %d\n",
>> -                   err);
>> -            ret = AVERROR_UNKNOWN;
>> -            goto copy_fail;
>> -        }
>> +    unmap_data = av_mallocz(sizeof(*unmap_data));
>> +    if (!unmap_data) {
>> +        ret = AVERROR(ENOMEM);
>> +        goto copy_fail;
>> +    }
>>   
>> -        offset += cpy.Height;
>> +    frame->buf[1] = av_buffer_create((uint8_t *)unmap_data, sizeof(*unmap_data),
>> +                                     nvdec_unmap_mapped_frame, (void*)devptr,
>> +                                     AV_BUFFER_FLAG_READONLY);
>> +    if (!frame->buf[1]) {
>> +        ret = AVERROR(ENOMEM);
>> +        goto copy_fail;
>>       }
>>   
>> +    unmap_data->idx = cf->idx;
>> +    unmap_data->idx_ref = av_buffer_ref(cf->idx_ref);
>> +    unmap_data->decoder_ref = av_buffer_ref(cf->decoder_ref);
>> +
>> +    for (i = 0; frame->linesize[i]; i++) {
>> +        frame->data[i] = (uint8_t*)(devptr + offset);
>> +        frame->linesize[i] = pitch;
>> +        offset += pitch * (frame->height >> (i ? 1 : 0));
>> +    }
>> +
>> +    goto finish;
>> +
>>   copy_fail:
>> -    decoder->cvdl->cuvidUnmapVideoFrame(decoder->decoder, devptr);
>> +    if (!frame->buf[1]) {
>> +        decoder->cvdl->cuvidUnmapVideoFrame(decoder->decoder, devptr);
>> +        av_freep(&unmap_data);
>> +    } else {
>> +        av_buffer_unref(&frame->buf[1]);
>> +    }
>>   
>>   finish:
>>       decoder->cudl->cuCtxPopCurrent(&dummy);
>> @@ -526,6 +560,7 @@ int ff_nvdec_frame_params(AVCodecContext *avctx,
>>                             int dpb_size)
>>   {
>>       AVHWFramesContext *frames_ctx = (AVHWFramesContext*)hw_frames_ctx->data;
>> +    AVCUDAFramesContext *hwctx = (AVCUDAFramesContext*)frames_ctx->hwctx;
>>       const AVPixFmtDescriptor *sw_desc;
>>       int cuvid_codec_type, cuvid_chroma_format;
>>   
>> @@ -550,6 +585,8 @@ int ff_nvdec_frame_params(AVCodecContext *avctx,
>>       frames_ctx->height            = (avctx->coded_height + 1) & ~1;
>>       frames_ctx->initial_pool_size = dpb_size;
>>   
>> +    hwctx->flags = AV_CUDA_HWFRAMES_DUMMY_MODE;
>> +
>>       switch (sw_desc->comp[0].depth) {
>>       case 8:
>>           frames_ctx->sw_format = AV_PIX_FMT_NV12;
> 
> Probably breaks if the API user doesn't use this dummy flag.

It intentionally stores the other buffer_ref in buf[1] so it doesn't 
leak that memory if the context is supplied externally.
It'll just be pointlessly wasting memory.

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