Which CPU type for Ryzen 5900X W11 guest on latest proxmox


Dec 15, 2020

Previously had guest set up with cpu host,hidden=1 flags but after latest round of gpu (passthrough nvidia gpu) driver upgrades, win11 upgrades and proxmox upgrades I am getting 8 fps in games and very unstable os performance

On a whim I changed cpu type to KVM64 and everything got much better


I can help feeling that there is a better cpu arg config that I should be using on this 5900X

Any help please?

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also on cpu type host I get alot of these warnings/errors

[11033.060489] SVM: kvm [46481]: vcpu0, guest rIP: 0xfffff87239a02ae9 unimplemented wrmsr: 0xc0010115 data 0x0
I have the same issue, with EPYC 7413 cpu. Performance increases immensely after changing CPU type to KVM. Also the aforementioned error wrmsr error disappears.
I assume it runs HyperV ontop and when I put KVM64 it doesnt do that and gets faster?


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So it's not just me??!!

I bought a AMD Ryzen 7 5800H with 32GB and NVME. It comes out of the box with Windows 11 Pro. I tested it and it ran amazing before I wiped and installed Proxmox.

I'm now on my 3rd install of a Windows 11 Pro VM. Running it with 16GB of ram [balloon=0], 14 cores [numa=1], virtIO SCSI, Writeback, virtIO NIUC. If I load Chrome, it takes 3 seconds to load, clicking the Start button takes 1 second before it pops up. W

hen I do speedtest.com, it shows me 150megabit speed on my 1gigabit line (though when I do a multi-threaded FTP download, it will ramp up to 600megabit). Doing a speedtest from Proxmox shows me 800+ megabit.

I have nothing else running on the machine and still have horrible Windows speed.

I now moved from Host to kvm64 and it's still slow.


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Disable Virtualization-based security, you can check if Running from msinfo32.exe.
It was off on Windows 10. (except Enterprise version iirc)
Disable Virtualization-based security, you can check if Running from msinfo32.exe.
It was off on Windows 10. (except Enterprise version iirc)
Are you sure this just expected slowdown of double hypervisors?
I saw this issue popping up online, mostly I saw mentions of it being fixed in previous linux kernel updates, and some mentions of some cpu flags in order to make Windows think that it is not running under a hypervisor (-hypervisor?).

By this issue, I mean the missing MSR message. I hope its not a red herring.

Also, I saw people mentioning this problem only happening when Nvidia GPU is passthrough'd (which is the case for both OP and me). I'll check if this reproduces with no GPU and then update.

Also, an interesting thread: https://www.reddit.com/r/VFIO/comments/z4o3oj/performance_hit_when_enabling_hyperv_on_windows/
They mention its AMD shenenigans making double hypervisors work real slow (something about interrupt mapping), and that the WRMSR message isn't really interesting.

Also this thread - https://www.reddit.com/r/Proxmox/comments/zjmz23/enable_a_nested_hyperv_in_a_windows_11_running_on/
Maybe when nested virtualization is configured properly Windows wise, then it will be fast instead of a broken HyperV that doesn't use any CPU virtualization features (same as using a 2014 CPU that has no MBEC). I will update my findings

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args: -cpu 'host,hv_ipi,hv_relaxed,hv_reset,hv_runtime,hv_spinlocks=0x1fff,hv_stimer,hv_synic,hv_time,hv_vapic,hv_vendor_id=proxmox,hv_vpindex,kvm=off,+kvm_pv_eoi,+kvm_pv_unhalt,+pdpe1gb,-hypervisor,+svm'

Seems to run well.
Just as an update to this.

I purchased an AMD Ryzen 7 5800H with 32GB and NVME mini PC and installed Proxmox and then a VM of Win 11.

Win 11 ran very poorly. Apps would take a few seconds to respond to clicks, Windows boot took a few minutes, etc. I tried installing Proxmox from scratch, AMD kernel, changing VM configs to host, KVM64, and more. I even gave the VM almost all the resources and nothing made it better.

So I went out and bought an i7-12650H with 32GB and NVME mini PC.. and it's like night and day difference. Windows is running at full speed. No delays in loading, windows opening, mouse clicks, etc.

I will be purchasing more computers for Proxmox, but will avoid AMD for now.


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