the phenomenon is specific to
Einstein@Home...you need to run multiple WU's simultaneously in order to max out GPU load. i used to have 4 GTX 560 Ti's on Einstein@Home, and it seemed their sweet spot for maximum GPU utilization was 3 simultaneous BRP tasks. now i have 3 GTX 580's (would like to add a 4th real soon), and their sweet spot on the E@H project seems to be 4 simultaneous BRP tasks. GPU load is hovering between 85-90% with my fan speed gonig at 85%. Running around 60c load. I did some SETI and Milkyway. Now I'm back over to Einstein to go for a while. Might leave it running on it next couple of days.
now you may have noticed that up until recently, an E@H BRP task typically consumed approx. 250MB of VRAM, and occasionally VRAM consumption would spike at just over 300MB, on an nVidia GPU in Windows. this may have changed a bit since the new Perseus Arm Survey began...in fact, as i reference my GTX 580 crunchers in MSI Afterburner, it appears that the new Perseus Arm Survey BRP tasks consume closer to ~180MB VRAM each. nevertheless, i experimented with both the 1.5GB and 3GB versions of the GTX 580 to confirm this, and i did it before the new Perseus Arm Survey tasks showed up. in other words, i experimented w/ GPU tasks that consumed ~250MB VRAM on average, and occasionally spiked at 300+MB VRAM. anyways, the reason i bring this up is b/c you'll most likely max out GPU utilization before you max out VRAM usage. you see, while the GTX 580 3GB mathematically had enough VRAM to manage up to 12 simultaneous BRP tasks (perhaps only 8 or 9 if you take VRAM spiking into consideration), GPU utilization would max out with only 4 simultaneous BRP tasks running. at that point i knew that a GTX 580 3GB was of no benefit over a GTX 580 1.5GB when it comes to maximizing GPU utilization on the Einstein@Home project.
keep in mind that this is no longer necessary with Einstein@Home. if you go to your Einstein@Home account and click on "Einstein@Home preferences" in the preferences section, you'll see something called "GPU utilization factor of BRP apps." this is the changeable parameter that allows you to run more than one task at a time (you no longer need to create an app_info.xml file to run multiple simultaneous tasks on the E@H project). it works just like it did in the app_info.xml file - that is, it uses the reciprocal method (a factor of 1 equates to running a single task, a factor of 0.5 equates to running 2 simultaneous tasks, a factor of 0.33 equates to running 3 simultaneous tasks,and so on and so forth).