Profler: cpu usage displays low usage per sceond

I make a every simple scene just for testing. To let FPS more stable, I enable Every V Blank. But I still find occasional frame drop. And I also find a phenomenon that there is a low cpu usage and high GPU usage every second. Why? cpu usage and GPU usage is every low!

@xujiezhige

This is the support forum for the Unity Analytics service. I think your post might get more attention on another section:

You’re reading it backwards, those are framerate increase spikes.

May be I should try Time.smoothDeltaTime.