I am using GPU rendering and my CPU is really bottlenecking blender down to only 50% of max GPU performance, while blender is taking up more than 90% of my CPU usage. How can I put less strain on my CPU so it will stop bottlenecking my GPU?
Even if you are rendering on GPU that does not mean evetything runs on it.
And things like physics, BVH creation, etc has to be made via CPU still.
So if your CPU is a bottleneck that is likely to happen always.
The only thing you can do is lower the number of threads Blender uses:
That will release CPU power but may slow the render
If 90% of CPU load bothers you, ie its not comfortable to work with other programs, you can set priority to the Blender by Task Manager.
Press Ctrl+Shift+Esc to launch Task Manager.
Prior Windows 10, right click on Blender process->Set Priority->Low. In the Windows 10 select details tab, and again right click on Blender process->Set Priority->Low