Could someone explain FPS capping resulting in less multi GPU usage to me?

[Goose]

Sorry if my topic isn't very clear, wasn't sure how to word it exactly.

I bought a second 280x to go Crossfire recently and in GTA 5 temps are getting to the mid 80's on the top card. I decided to limit the FPS to 57 in RivaTunerSS as I heard this can help with stutter and tearing etc. With the FPS limit in place GPU usage is at about 60% on both cards and temps are good 10-15c lower which is great.

Now I understand that usage and temps are lower because the card isn't attempting to pump out as many frames as it can, what puzzles me is that when my FPS actually drops to 50 or so when driving GPU usage doesn't increase to try and get back to 57.

Could anyone enlighten me on how GPU usage actually works when FPS capping?

Thanks

 

[varkanoid]

Show us the GPU usage at 50fps, (ie show the graphs you are looking at)

 

[Rroff]

Could be CPU (either insufficient or due to API or threading bottlenecks) can't feed the GPUs fast enough.

 

[Goose]

Thats the thing though, if i dont frame cap then GPU usage is 100% on both cards.