Forgot to mention, I kept seeing the MHash drop off when the screen would disable even though I configured Ubuntu to ignore all power saving settings; whenever I'd wake the screen up by jiggling the mouse or hitting a keystroke, it would be sub-300 but then on the next workunit jump right back up to 312+.
My solution, since this is a dedicated mining rig, was to set the session to xterm, and use AMDOverdrvCtrl with the -b flag to load a saved .ovdr profile followed by calling out Phoenix. In this way I was able to eliminate the performance drop, and also since I have the system on UPS and set to auto-reboot / auto-logon, I basically have a bulletproof bitcoin dispenser
My solution, since this is a dedicated mining rig, was to set the session to xterm, and use AMDOverdrvCtrl with the -b flag to load a saved .ovdr profile followed by calling out Phoenix. In this way I was able to eliminate the performance drop, and also since I have the system on UPS and set to auto-reboot / auto-logon, I basically have a bulletproof bitcoin dispenser
Are you sure the hash rate was actually dropping while the screen was off? I've noticed in Windows 7 that waking the screen by moving the mouse causes a brief ~10-20% dip in GPU utilization (seems to be true for both ATI and nvidia cards). I have no idea about Linux really, but could it be possible it's just a blip as the screen comes back on? Another workaround would just be to set the screen to always on and turn it off yourself - something I have to do because one of my Dell screens audibly beeps while in standby mode (?!)