FPS display in game

I am looking for an explanation of what are the value we see in the FPS display in game and what is affecting what value.
FPS, I am ok with, but what is main-t representing and is it more representative of GPU or CPU and what is affecting it, bad optimization, too many AI,...?
I looked for an existing thread, as I thought I have seen an explanation before, but could not find it.

 

main t = main CPU thread, too many AI affects it the most probably.

 

yes, we all know AI affect mostly CPU.
So if main -t says 78%, it means CPU usage is 78%?
How about the other numbers, is there one showing the GPU occupancy?
Surely there must be a detailed explanation of what does what and why, somewhere.

 

Ft=CPU latency
CPU/maint t = CPU usage
Dip=GPU drawns ( iirc)
TRI= number of "triangles" being rendered in the screen (iirc)
b.size=buffer size
scene=?
phy= physics thread usage
fmod dsp=dsp usage in fmod
fmod usage = total fmod engine/thread usage

 

MAIN-T is rendering thread CPU usage.
From Stefano a while back.

Render Stats App
---------------------------
FPS - Frames Per Second, your framerate
FT - Frame Time, time in milliseconds for how long a frame takes to render
Main_T - see below
DIP - Number of draw calls (not really important to the average player) DIP the better the performance in general, Indicating Optimized game assets like tracks, cars)
TRI - Total number of triangle polygons
B.Size - Average size of draw call batches (again, not important to the player but the lower the better)
SCENE - Tri count of the scene (after culling) on screen
PHY - see below
PHY_LATE - same as above, shoulderstand indicate the number of times physics calculation Took over 3 ms per frame
FMOD USAGE - FMOD is the sound engine used in AC. Not sure what the percentage exactly to but high values have impact on performance.

Main_T value is for the graphics thread. It shows the relationship between the time spent in the application (CPU) and the time spent to complete a frame (FRAME TIME). Values of CPU near 100% indicate a CPU-bound system graphically.
EX ... if a frame took 16ms to complete and CPU is 50% it means that AC was able to prepare the frame in 8ms .. and the GPU took 16ms to render it. (GPU bound) .. if CPU is 100% then it took the CPU 16ms to prepare the frame and the GPU is probably capable of faster (CPU bound).
No relationship whatsoever with the value read in task manager.
PHY is relative to the physics thread, values above 100% indicates that the system is not ready to calculate the physics in time (3ms per step) and that the game is now running slower than realtime (slowmo). Practically, there are too many AI and the CPU is not ready to handle it.