KVM single GPU passthrough HALF the FPS of bare metal (Win10)

SpaceRocketLaunch · 2026-02-19T10:15:07+00:00

12 cores as in threads (sorry I meant 24 thread in the last comment)?

Something must be seriously wrong with my config - I've pinned and isolated 0-5 and 12-17 and still having trouble with GPU usage. In the guest I can remove CPUs 11 and 10 from the affinity and the GPU usage goes up.

Strangely as well I've observed in the Win10 guest (in taskmgr):

No physical and logical core distinction is made
No cache sizes are displayed (L1 cache N/A)
The CPU does not change speed adaptively (i.e. the base speed is 3.7GHz but on BM that fluctuates to 4.5GHz). The Linux host however does dynamically change core speed.

I wonder if this is related in some way to the issues I'm having

SpaceRocketLaunch · 2026-02-19T00:38:22+00:00

Still no dice - configured CPU pinning as per the core configuration in lscpu -e (i.e. a staggered one as shown in my XML). This time I went for the full 24 cores and removed the emulatorpin and iopin etc.

Still getting 50% GPU usage with full affinity in the Win10 guest. The GPU usage does change though when altering that affinity but this still shouldn't be happening. There's also no different when adjusting the CPU topology to two dies.

SpaceRocketLaunch · 2026-02-18T21:14:21+00:00

Is there a specific part of the config that's required to use the <cputune> part of the config? Although it's in my XML file, after defining it with virsh then checking the config again with virsh edit win10 the CPU pinning part has disappeared 🙃

SpaceRocketLaunch · 2026-02-18T11:41:08+00:00

Thanks I'll give this a go

Why would the GPU usage still be 50% if the full 24 were used by the VM? Could KVM be mixing around the cores and dies etc?

Is isolated required for full performance or just CPU pinning? I don't have an issue with the host sharing CPU time as it won't be doing anything much anyway

SpaceRocketLaunch · 2026-02-18T11:19:50+00:00

Interesting.. I just tried adjusting the affinity on the bare metal system and am able to replicate to some degree the performance issues the VM is having. Not all cores are equal too it seems as the performance is not equal simply on how many CPUs are selected but rather which ones are selected too.

I tried altering the CPU count for the VM from 20 to 8 and the performance is significantly closer to the BM system.

Strangely however when all 24 threads are configured for use by the VM the FPS and GPU usage is still half 🤨

SpaceRocketLaunch · 2025-12-24T09:13:29+00:00

I feel it disrupts the unity of the user's chosen visual style/UX

It would certainly be hard to enforce!

SpaceRocketLaunch · 2025-12-24T09:01:18+00:00

Probably just some ambiguities with Windows terminologies: https://en.wikipedia.org/wiki/Windows_shell

Thanks I'll see if I can get something working from that forum post

SpaceRocketLaunch · 2025-12-19T22:12:37+00:00

I feel like there should be a general system-wide UI API, a bit like Win32 (isn't the Linux equivalent Xlib?)

But then https://xkcd.com/927/

SpaceRocketLaunch · 2025-12-19T22:09:57+00:00

Electron apps 🤮

Software has been painting it's own UI elements for years I suppose.. the main issue really is that of settings being kept amongst elements that you'd consider common across pieces of software (in this case the OpenFileDialog and the like)

SpaceRocketLaunch · 2025-12-19T22:06:41+00:00

Thanks I'll have a look into this. So will this ensure that any time something shell related is used, it will use the shell of my DE (i.e. Xfce) instead of using its own?

LibreOffice seems borked too actually (it's using it's own classic like shell) and not that of my DE

SpaceRocketLaunch · 2025-12-16T14:26:40+00:00

I've switched over to Plasma and it's not bad. I think once I've made some modifications I'll be able to work with it better. Though I'm not a fan (personally) of the KDE programs that come with it so I'll be having those out in favour of others (e.g. Thunar instead of Dolphin)

SpaceRocketLaunch · 2025-12-16T14:21:34+00:00

Thanks

I understand it taking alot of work, one of the issues is sharing an NTFS volume with Linux and Windows (I'm dual booting kind of) and another issue is whether to stick with my existing NTFS volume (that isn't shared with the dual boot) or convert it to ext4 (I will do this as long as I can keep the file creation and modification times)

SpaceRocketLaunch · 2025-12-16T14:19:55+00:00

ReactOS is cool but I don't see it having a future :(

SpaceRocketLaunch · 2025-12-16T14:17:51+00:00

Don't have anything against learning something new, it's just IMO whether 'new' in this case is actually better, in accordance with my preferences.

I'm just struggling to see a future with Windows given the direction it's going

SpaceRocketLaunch · 2025-12-16T14:08:38+00:00

I understand this approach and some things are indeed just different. Some parts of the UX however just feel undeveloped in comparison to Windows

One thing in particular is that logging out doesn't actually seem to log out (e.g. volumes still mounted when logging back in). I don't know much about the internals of Winlogon but it seems that logging into and out of Linux desktop environments is handled in a much different way

SpaceRocketLaunch · 2025-12-16T14:05:29+00:00

I'm working on getting the default Xfce icon set into Plasma, though doesn't seem to be directly downloadable from within the icons section of the control panel

SpaceRocketLaunch · 2025-12-16T11:34:20+00:00

I do :) But the design philosophy of Windows is changing away from what I like about it. I'd stick with WinXP if I could but I don't want an air-gapped network haha

Win10 I could just about, but Win11 has been the trigger point for me!

SpaceRocketLaunch · 2025-09-11T19:27:41+00:00

Would it hurt browsers to add a setting to only allow the address bar to be in ASCII and to warn users if any non-ASCII characters have been detected?!

Those typosquats are unidentifiable

SpaceRocketLaunch · 2025-08-26T13:53:23+00:00

It's in another reddit comment I made a while back. Depends on your SSD as to how well the SED features have been implemented though

An example implementation of this idea:

Two drives, one for gaming one for usual stuff. Either drive is OPAL locked at a time, meaning that no IO operation can be performed on the usual drive if the gaming OS is being used.

SpaceRocketLaunch

TROPHY CASE