If you feel little breaks in moving the mouse pointer or any other stuttering on the gui during I/O operations, here is how to tweak kernel preemption to improve user experience in smooth running of the gui.
You have to set two kernel parameters with the help os sysctl(7):
Defaults to 128. I have tried 256, and goes well.
Defaults to 0,. I set up to 64.
Test your results, then read the documentation of the scheduler on the link attached.