After not much optimization, the Valve Linux team found the Linux version of Left 4 Dead 2 outperformed its Windows version by 16.7%, which translates to an extra 45 frames per second on their Core i7 test PC.
Interestingly, the first Linux build of Left 4 Dead 2 ran at a meager 6 FPS (frames per second). The team then spent a few months optimizing the game for Linux Kernel and OpenGL. The results were impressive as the game ran flawlessly at 315 FPS.
On the same test PC that comprises an Intel Core i7 3930k CPU and an NVIDIA GeForce GTX 680 GPU, the Windows 7 version of the game ran at 270 FPS only in DirectX mode.
"Why does an OpenGL version of our game run faster than Direct3D on Windows 7? It appears that it's not related to multitasking overhead," Valve's Linux team wrote on their official blog. "We have been doing some fairly close analysis and it comes down to a few additional microseconds overhead per batch in Direct3D which does not affect OpenGL on Windows. Now that we know the hardware is capable of more performance, we will go back and figure out how to mitigate this effect under Direct3D."
The team ported some of the Linux OpenGL optimizations to their Windows version of the game, boosting its frame rate to 303.4 FPS in OpenGL mode.