Hi everyone,
In order to avoid the performance penalty of using host (md_clear, flush_l1d), I started using 'x86-64-v4' which works perfectly but I can't pass hypervisor flags to Windows VM. I tried creating custom cpu configuration using( cpu base, EPYC-Genoa, etc..) and add/removing cpu flags, but the performance is still unbearable compared to x86-64-v4.
Setup:
I have a Ryzen 9 9950x3d, 5090, x870e crosshair hero on my Pve 9.0.11 on all the latest updates.
Host( slow performance)
x86-64-v4:
EPYC-Genoa(has no md_clear, flush_l1d but is still slower than x86-64-v4) :
In order to avoid the performance penalty of using host (md_clear, flush_l1d), I started using 'x86-64-v4' which works perfectly but I can't pass hypervisor flags to Windows VM. I tried creating custom cpu configuration using( cpu base, EPYC-Genoa, etc..) and add/removing cpu flags, but the performance is still unbearable compared to x86-64-v4.
Setup:
I have a Ryzen 9 9950x3d, 5090, x870e crosshair hero on my Pve 9.0.11 on all the latest updates.
Host( slow performance)
Code:
affinity: 0-7,16-23,8-15,24-31
args: -cpu host,-hypervisor,kvm=off, -smbios type=0,vendor="American Megatrends Inc.",version=1715,date="09/19/2025"
balloon: 0
bios: ovmf
boot: order=sata0
cores: 32
cpu: host,hidden=1
efidisk0: local:112/vm-112-disk-0.raw,efitype=4m,pre-enrolled-keys=1,size=528K
hookscript: local:snippets/power-mode-hook.sh
hostpci0: 0000:01:00.0,pcie=1,x-vga=1
hostpci1: 0000:01:00.1,pcie=1
hostpci2: 0000:0d:00,pcie=1
ide2: local:iso/Win11_24H2_English_x64.iso,media=cdrom,size=5683090K
machine: pc-q35-10.1
memory: 32800
meta: creation-qemu=10.0.2,ctime=1757533697
name: Win11
numa: 1
ostype: win11
sata0: local:112/vm-112-disk-1.raw,cache=writeback,size=286G,ssd=1
smbios1: REDACTED
tpmstate0: local:112/vm-112-disk-2.raw,size=4M,version=v2.0
vga: none
vmgenid: REDACTED
root@horsepower:~#x86-64-v4:
Code:
affinity: 0-7,16-23
args: -cpu x86-64-v4,kvm=off,-hypervisor -smbios type=0,vendor="American Megatrends Inc.",version=1715,date="09/19/2025"
balloon: 0
bios: ovmf
boot: order=sata0
cores: 16
cpu: x86-64-v4,hidden=1
efidisk0: local:112/vm-112-disk-0.raw,efitype=4m,pre-enrolled-keys=1,size=528K
hookscript: local:snippets/power-mode-hook.sh
hostpci0: 0000:01:00.0,pcie=1,x-vga=1
hostpci1: 0000:01:00.1,pcie=1
hostpci2: 0000:0d:00,pcie=1
ide0: local:iso/gparted-live-1.7.0-8-amd64.iso,media=cdrom,size=580M
ide2: local:iso/Win11_24H2_English_x64.iso,media=cdrom,size=5683090K
machine: pc-q35-10.1
memory: 32800
meta: creation-qemu=10.0.2,ctime=1757533697
name: Win11
numa: 1
ostype: win11
sata0: local:112/vm-112-disk-1.raw,cache=writeback,size=286G,ssd=1
smbios1: REDACTED
sockets: 1
tpmstate0: local:112/vm-112-disk-2.raw,size=4M,version=v2.0
vga: none
vmgenid: REDACTEDEPYC-Genoa(has no md_clear, flush_l1d but is still slower than x86-64-v4) :
Code:
affinity: 0-7,16-23
args: -cpu EPYC-Genoa,-la57,hv_vendor_id=null,-hypervisor -smbios type=0,vendor="American Megatrends Inc.",version=1715,date="09/19/2025"
REMOVED
cores: 16
cpu: EPYC-Genoa,-la57,hidden=1
REMOVED- I can't pass in hypervisor/kvm=off flags without Proxmox bootlooping.
- I can't pass args '-cpu x86-64-v4 ' without Proxmox bootlooping/not starting.
- I tried starting from cpu 'base' and adding x86-64-v4 cpu flags and some flags aren't found.
- I tried using qemu64/kvm64 and some flags aren't found.
Last edited: