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

Dennis Mungai dmngaie at gmail.com
Mon Mar 30 15:39:43 EEST 2020


On Mon, 30 Mar 2020, 15:31 Dennis Mungai, <dmngaie at gmail.com> wrote:

> On Mon, 30 Mar 2020, 15:22 Valentin Schweitzer, <vs at nativewaves.com>
> wrote:
>
>> 1234567890123456789012345678901234567890123456789012345678901234567890
>>
>> 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.
>


One more thing: Could you show us the output of:

numactl --hardware


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