Off-screen mode doesn't reach the full occupancy rate of the GPU

[didiHe]

I tested Nvdia and AMD GPU in Linux. When Nvidia GPU is in test, I use "watch -n 5 nvidia-smi" to check the GPU occupancy rate. In on-screen mode the occupancy rate can reach 100% but in off-screen mode , the rate only reach to 80%. Same as AMD GPU, the "Graphics pipe" can reach 100% in on-screen mode, about 60%~80% in off-screen mode.

I feel confused about the result. Since the score of off-screen is much higher than on-screen. What kind of program occupy GPU in on-screen mode?