Poor Linux Performance - thoughts why?

[Burstaholic]

I decided to give Dolphin a try the other day in Kubuntu, and discovered that it had serious performance trouble with 'Internal Resolution' set at anything above Native. On my 1080p laptop with 'match window resolution' set, Smash Bros. Melee barely managed 17 FPS. Since this is an Optimus laptop, I tried it with primusrun to use the discrete card, and was shocked to find my FPS crashed down to about 7 FPS.

I decided to reboot into Windows 7, since that seems to be the primary target platform, and lo and behold, steady 60 FPS even on the integrated Intel. Clearly, not a problem of insufficient hardware.

Does anyone know why there's such a vast performance difference between Linux and Windows on the same hardware? Searching the forums found a few others complaining about Linux performance, but no real discussion or resolution.



Gritty details:
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On Kubuntu I built from GitHub master due to the lack of a current package, while on Windows I grabbed the latest zip from the build page. I can go back and find exact revision numbers if needed, but I discovered the same issue with straight 4.0.2 on my Arch/Windows desktop later, so it's been around a while.

Hardware:
Intel i7-3610QM 2.3GHz - 3.3GHz
Nvidia 675M
12 GB RAM DDR3