A comprehensive and step by step guide can also be found in the Arch Linux Wiki.
There are also some hints for tuning the KVM as well as troubleshooting tips.
One important step for my setup for example was to allocate the memory for the KVM via hugepages.
I’d recommend synergy to everyone.
For anyone who wants to keep the costs down or just wants to try the program before buying:
The program can be compiled from github sources. If you don’t know what that means just buy the program.
I usually start my vm with a script that allocates the 10gb of hugepages, sets the cpu governor to performance and deactivates the screen in linux that will be used for the vm.
This way the vm starts and the passed through gpu delivers its input to that monitor.
I have Synergy keybindings to switch from host to client and vice versa as well as a keybinding to lock screen border so that the mouse doesn’t go over to the other screen when I move it to the side.