I ran into similar issues with Windows 10 (1803), with regard to 2D graphics performance.
See my bug report here: https://bugzilla.kernel.org/show_bug.cgi?id=200877
Could you test with Spectre protection (temporarily) turned off inside the Windows VM?
See my post here: https://heiko-sieger.info/low-2d-graphics-benchmark-with-windows-10-1803-kvm-vm/
I ran into similar issues with Windows 10 (1803), with regard to 2D graphics performance.
See my bug report here: https:/ /bugzilla. kernel. org/show_ bug.cgi? id=200877
Could you test with Spectre protection (temporarily) turned off inside the Windows VM?
See my post here: https:/ /heiko- sieger. info/low- 2d-graphics- benchmark- with-windows- 10-1803- kvm-vm/