[FFmpeg-user] High CPU usage during scale_npp to low resolutions with multiple instances

[Dennis Mungai]

On Mon, 30 Mar 2020, 15:22 Valentin Schweitzer, <vs at nativewaves.com> wrote:

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>
> Hi,
>
> when using scale_npp to scale a test video down from 1920x1080 to
> 1024x576 or lower with multiple processes in parallel, CPU usage is
> unusually high.For context, when scaling the same video down to
> 1280x720, CPU usage stays at about0.5% per FFmpeg instance. When
> scaling down too 1024x576 or lower, CPU usage per FFmpeg process rises
> to about 3.0%. The values listed here appear when starting 29
> instances of FFmpeg in parallel. The effect is less pronounced but
> still visible at 10 instances in parallel. Hardware used for this
> is an AMD EPYC 7401P 24 Core + NVIDIA Quadro RTX 4000.
>
> To generate 100s of random noise in 1080p (which will be the test video):
>
> ffmpeg -y -hide_banner -f lavfi -i nullsrc=s=1920x1080 -filter_complex
> "geq=random(1)*255:128:128;aevalsrc=-2+random(0)" -vcodec rawvideo
> -acodec pcm_s16le -t 100 noise.mkv
>
> Now rescale the test video to 720p:
>
> ffmpeg -hide_banner -y -i noise.mkv -vf
> hwupload_cuda,scale_npp=w=1280:h=720:format=nv12 -vcodec h264_nvenc -an
> -f null NUL
>
> This should not cause very high CPU usage. Now rescale the same video to
> 576p:
>
> ffmpeg -hide_banner -y -i noise.mkv -vf
> hwupload_cuda,scale_npp=w=1024:h=576:format=nv12 -vcodec h264_nvenc -an
> -f null NUL
>
> This should cause about 5 or 6 times as much CPU usage.
>
> This might be caused by some NVIDIA optimizations, but it does not
> seem to be documented and I have yet to find a good place to ask
>


Set this environment  variable: CUDA_DEVICE_MAX_CONNECTIONS=2

Then retest and report back.

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