The first step is identifying which function is responsible for the invokePV call. The most likely in this case is glfwSwapBuffers(), so you should verify that.
Probably, due to the waiting associated with vsync and swapping buffers. After sampling CPU usage on my dev PC, where CPU usage was still ~0.5%, the sampled values were very similar to the above, so it's probably not invokePV.
EDIT: I've run some testing with and without vsync.
With vsync: Avg 48fps/10ms per frame, 7% cpu usage
Without vsync: Avg 60fps/0ms per frame, 3% cpu usage
With vsync, expected frame time is ~16ms per frame, though with a lower fps, this value can be distorted
Without vsync, cpu time of invokePV becomes negligible