I have the same problem, but my CPU Scaling is set to Performance, so changing that didn't solve the problem. The CPU usage and RAM usage in task manager inside the Windows VM show low to medium usage, and the usage shown in Unraid is also equally low, and yet the Windows VM is super choppy and laggy even in things as simple of opening file explorer or simple web browsing. It was running perfectly fine before the upgrade to Unraid 6.9.1, so that's the only thing I can think of that could have caused this. It seems so weird that it would lag like that when the CPU usage, RAM usage, Disk usage, etc. are all fairly low according that task manager and Process Lasso in Windows, and the CPU clock speed is at 4.8 GHz (checked using `grep MHz /proc/cpuinfo` in the unraid terminal).
Edit: After updating from 6.9.1 to 6.9.2, the problem seems to be fixed. I will come back and add more if the problem reappears
Edit 2: The problem came back about a day later, it is intermittently lagging with occassional moments of perfect smooth performance. I have tested while viewing the resource usage in Unraid and there is no correlation at all between changes in Unraid CPU usage or memory usage vs. the weird lag inside the VM, and same with the resource usage reported by task manager. It is like there is a bottleneck somewhere, but there is not sign of additional load anywhere and it was running flawlessly on Unraid 6.7.X and 6.8.X,
I also tried update the VFIO guest drivers, and updating graphics driver in Windows, neither of those had any impact on the problem
I may make a separate thread for my scenario, since my computer's symptoms are now starting to deviate from the OP of this thread