I have Steam installed along with CS:GO, HL2, and Payday 2, and this happens in all of the games: when I start a game, the game seems to run fine at over 60 FPS. Then, the game starts to stutter, to the point where there are severe FPS drops (2 FPS).
I am running a Core i5-2520M (dual-core hyper-threaded) with HD 3000 graphics. In Windows, I get lower FPS (30+) on my games, but I have never seen frame drops like the ones I'm getting on Ubuntu. In fact, everything always ran smoothly. I don't know whether this is an issue with the drivers, or it's an issue with thermals.
The Additional Drivers tab shows:
The output of top shows:
What can be done to fix this?