I have 2 monitors hooked up to my PC (one Dell 1920x1080 / 60hz and one Viewsonic 1680x1050 / 60hz) and I extend my desktop to the Viewsonic so that I can keep an eye on my web browser / IM / music player while I play games. I recently installed a 2nd 5850 to check out crossfire for the first time. Doing so has allowed me to get nearly twice the frames per second in many of my games at 1920x1080 and max settings, including Dirt 3 and Crysis. This has made it more important for me to enable the v-sync in many games to keep it locked at 60 fps and avoid excessive tearing.
Here's the problem... if I have crossfire enabled while I'm doing my dual monitor setup, the v-sync in games seems to become capped at 30 fps rather than 60 fps. This ONLY happens when crossfire is enabled AND I am extending my desktop to my second monitor. If I disable crossfire, the v-sync works at 60 fps. Alternatively, if I keep crossfire enabled and disable my 2nd monitor, the v-sync also works at 60 fps. I have tested this with Dirt 2, Dirt 3, Just Cause 2 (demo), and Crysis.
Something about running crossfire while gaming with my desktop extended to a second monitor is breaking the functionality of the v-sync option for these games (and many others I'm assuming). It is important to note that with crossfire enabled, the performance of these games with the v-sync turned off is NOT affected by whether or not I have both monitors connected.
One more interesting bit: during benchmarks (with crossfire on and dual monitors) if I enabled the v-sync and clearly see the game running at only 30 fps, the benchmark results still report 60 fps.
Does anybody have any idea why the combination of crossfire and a dual monitor setup makes v-syncs in games dysfunctional?
What games do you play, and you do have the v-syncs on, yeah? Also, if you could tell me a little bit more about your setup it could be helpful.
I have both monitors plugged into my first 5850, both with DVI.
I have the following system:
Gigabyte GA-X58A-UD3R motherboard
i7 920 @ 4.0 GHz
XFX HD 6950 2Gb reference card unlocked shaders
MSI R6950 Twin Frozr II using MSI's unlocked 6950 Twin Frozr III PE BIOS
LG Flatron W2452T 24" 1920x1200 60hz monitor
SyncMaster930a 21" 1280x1024 60hz monitor
The 24" is my primary monitor with the 21" as my extended desktop.
Games? I have a lot
I've been playing these most recently:
Dragon Age II
The Witcher 2