I get the same thing, GTX 980ti here. Total UI slowdown. Mouse moves in slow motion, jerky.

from topic link to post http://asteroidsathome.net/boinc/forum_thread.php?id=494&postid=5033#5033

Noticed last week also a sudden mouseLAG. It's only when the mouse-arrow is on the desktop-wallpaper and no lag when arrow moves over into a window of a program.
Noticed also that lag is also gone when pressing the "go desktop" (lower-right corner besides the vertical bar).
-Tried 1st going back to older usb 3.0 drivers (updated those the same day as I noticed the lag the 1st time).
-Went back a version of BOINC (7.6.22 now), didn't helped still lag on the older.
-Went back to the latest certified GeForce ROG-drivers on Asus website (359.06)coz I've an Asus Matrix 980ti. Still lag atm.

Lag is gone as soon I pause project and/or the gpx-card crunch other projects.
Is there a fix for this?

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Not really. GPU applications that fully utilize the GPU will have screen lag. I mean like 99-100% full GPU utilization. I've seen it on several projects like Asteroids, Collatz and FAH. Others like E@H with a bit lower GPU util do not have screen lag.

Basically, CPUs have interrupts but GPUs do not. Keyboard input is an interrupt that gets to move to the head of the work queue for CPUs. Since GPUs are meant to display live images and originally weren't designed as compute engines for other things besides drawing images on a screen, there is no GPU interrupt. Any input or change to the screen has to go through the work compute buffer before getting to your mouse movement. Also unlike CPUs you can't tell it to run at 90% either.

If you're not gaming at the moment, the screen could be powered off the iGPU instead of the 980Ti.

If you notice issues with GPU crunching while using the computer, you can edit your computing settings to disable GPU computing while the computer is in use. I will pause GPU computation manually when watching videos, since I have my "in use" settings to be keyboard/mouse activity in the last minute.

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Telling your mouse utility to use a lower report rate solved this issue for me. Switching the report rate from 1 kHz to 125 Hz (the de facto default report rate for non-gaming USB mice) on my Logitech G502 Proteus Core solved the issue for me.

If you notice issues with GPU crunching while using the computer, you can edit your computing settings to disable GPU computing while the computer is in use. I will pause GPU computation manually when watching videos, since I have my "in use" settings to be keyboard/mouse activity in the last minute.

You can also enable option "Suspend GPU computing when computer is in use" and set delay in next field to 5 secs (0.08). This worked well for me during normal work. For video watching manual suspend will be better.

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