To start, the relevant hardware/software information:
The problems:
-ghost keys: I've tried 2 different keyboards: one USB, and the other PS/2 - it makes no difference. When walking around and I lift my finger off a movement key, the character keeps walking. Thankfully this one can be stopped by pressing the offending key. I even get random keypresses - the game might pause, open a character stat window, or melee attack without me even pressing the button at all. This happens on the mouse, too. Sometimes I'll release left click and my character keeps shooting, and the mouse sensor stops working entirely. I can't even look around. And even worse, unlike the keyboard ghost keys, I can't make it go away by pressing a button. The mouse completely stops working, and I just have to wait for it to sort itself out. Like the previous issue, this only happens under load.
-display: This is somewhat irrelevant to the previous two, but I might as well kill 2 birds with 1 stone, as the saying goes. Please note that I do not advocate killing birds with stones. Anyway, would it be possible to route the display output of the RX 480 into a window on the host? Remember this is used for gaming, so RDP has too much latency.
-i5 4690k @ 4.2GHz, no hyperthreading, 3 out of 4 cores given to guest
-500GB SSD dedicated to host, 500GB HDD dedicated to guest (direct passthrough, no write caching)
-Intel HD graphics used for host, RX 480 passed directly through to guest
-16GB RAM on host, 8GB dedicated to guest
-VM is used for gaming, managed through virt-manager interface
-Windows 10 x86_64 guest, Kubuntu 16.10 host
-SPICE display
-Realtek AC97 audio device, drivers installed by rebooting with driver signatures disabled
-Emulated 16MB VGA card for the in-window display
The problems:
-random hitching: for some reason, every so often, the entire guest OS locks up for a moment. Sometimes the audio keeps going, sometimes it cuts out, and sometimes it loops the last tiny bit (what I assume is some kind of buffer), but it depends on the game really. MSI Afterburner (I have the graphs going on the fake "monitor" within the virt-manager window, and the games running off a physical monitor connected directly to the RX 480) shows a massive spike in the frametime graph (going from the normal 10-20ms all the way up to 500+ms). There seems to be absolutely no connection between this and any hardware utilization; no spikes in CPU, HDD, RAM, or networking. This only seems to happen while the system is under load, though.
-ghost keys: I've tried 2 different keyboards: one USB, and the other PS/2 - it makes no difference. When walking around and I lift my finger off a movement key, the character keeps walking. Thankfully this one can be stopped by pressing the offending key. I even get random keypresses - the game might pause, open a character stat window, or melee attack without me even pressing the button at all. This happens on the mouse, too. Sometimes I'll release left click and my character keeps shooting, and the mouse sensor stops working entirely. I can't even look around. And even worse, unlike the keyboard ghost keys, I can't make it go away by pressing a button. The mouse completely stops working, and I just have to wait for it to sort itself out. Like the previous issue, this only happens under load.
-display: This is somewhat irrelevant to the previous two, but I might as well kill 2 birds with 1 stone, as the saying goes. Please note that I do not advocate killing birds with stones. Anyway, would it be possible to route the display output of the RX 480 into a window on the host? Remember this is used for gaming, so RDP has too much latency.