50% NVDEC usage on T4

I see that there are two chips in T4, and I run the following command, the NVDEC usage can only be 50% at most

./ffmpeg -vsync 0 -hwaccel cuvid -c:v h264_cuvid -i ./long.mp4 -an -f null /dev/null


I would appriciate every advice, thanks

The nvdec usage raise 100% while running multiple ffmpeg command concurrently