I found your thread while discovering this issue myself.
My setup is cpu i9-12900k, Unraid version 6.12.13
Topology attached.
If i add more then 3 cores to my windows 11 vm i get bad stutters whenever i do anything heavy (like compiling) (funny enough, there is no stutter if i run cinebench)
Here is my xml
<?xml version='1.0' encoding='UTF-8'?>
<domain type='kvm' id='15'>
<name>Windows 11</name>
<uuid>77fe918b-c4ee-45b5-902f-b00928b24900</uuid>
<metadata>
<vmtemplate xmlns="unraid" name="Windows 11" icon="windows11.png" os="windowstpm"/>
</metadata>
<memory unit='KiB'>17301504</memory>
<currentMemory unit='KiB'>17301504</currentMemory>
<memoryBacking>
<nosharepages/>
<locked/>
</memoryBacking>
<vcpu placement='static'>6</vcpu>
<cputune>
<vcpupin vcpu='0' cpuset='2'/>
<vcpupin vcpu='1' cpuset='3'/>
<vcpupin vcpu='2' cpuset='4'/>
<vcpupin vcpu='3' cpuset='5'/>
<vcpupin vcpu='4' cpuset='6'/>
<vcpupin vcpu='5' cpuset='7'/>
<emulatorpin cpuset='0-1'/>
</cputune>
<resource>
<partition>/machine</partition>
</resource>
<os>
<type arch='x86_64' machine='pc-q35-7.1'>hvm</type>
<loader readonly='yes' type='pflash'>/mnt/cache/appdata/VM/ovmf/ovmf-x64/OVMF_CODE-pure-efi-tpm.fd</loader>
<nvram>/etc/libvirt/qemu/nvram/77fe918b-c4ee-45b5-902f-b00928b24900_VARS-pure-efi-tpm.fd</nvram>
<smbios mode='host'/>
</os>
<features>
<acpi/>
<apic/>
<hyperv mode='custom'>
<relaxed state='on'/>
<vapic state='on'/>
<spinlocks state='on' retries='8191'/>
<vendor_id state='on' value='none'/>
</hyperv>
</features>
<cpu mode='host-passthrough' check='none' migratable='on'>
<topology sockets='1' dies='1' cores='3' threads='2'/>
</cpu>
<clock offset='localtime'>
<timer name='hypervclock' present='yes'/>
<timer name='hpet' present='no'/>
</clock>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/local/sbin/qemu</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='writeback'/>
<source file='/mnt/cache/appdata/VM/domains/Windows 11/vdisk1.img' index='4'/>
<backingStore/>
<target dev='hdc' bus='virtio'/>
<serial>vdisk1</serial>
<boot order='2'/>
<alias name='virtio-disk2'/>
<address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
</disk>
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<source file='/mnt/cache/appdata/VM/isos/Win11_23H2_EnglishInternational_x64v2.iso' index='3'/>
<backingStore/>
<target dev='hda' bus='sata'/>
<readonly/>
<boot order='1'/>
<alias name='sata0-0-0'/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<source file='/mnt/cache/appdata/VM/isos/virtio-win-0.1.262.iso' index='2'/>
<backingStore/>
<target dev='hdb' bus='sata'/>
<readonly/>
<alias name='sata0-0-1'/>
<address type='drive' controller='0' bus='0' target='0' unit='1'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='writeback'/>
<source dev='/dev/disk/by-id/ata-APPLE_SSD_TS128C_31DS10JZTLMZ' index='1'/>
<backingStore/>
<target dev='hdd' bus='sata'/>
<alias name='sata7-0-0'/>
<address type='drive' controller='7' bus='0' target='0' unit='0'/>
</disk>
<controller type='usb' index='0' model='qemu-xhci' ports='15'>
<alias name='usb'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</controller>
<controller type='sata' index='0'>
<alias name='ide'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
</controller>
<controller type='sata' index='1'>
<alias name='sata1'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x0'/>
</controller>
<controller type='sata' index='2'>
<alias name='sata2'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x0'/>
</controller>
<controller type='sata' index='3'>
<alias name='sata3'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x04' function='0x0'/>
</controller>
<controller type='sata' index='4'>
<alias name='sata4'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x05' function='0x0'/>
</controller>
<controller type='sata' index='5'>
<alias name='sata5'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x06' function='0x0'/>
</controller>
<controller type='sata' index='6'>
<alias name='sata6'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x07' function='0x0'/>
</controller>
<controller type='sata' index='7'>
<alias name='sata7'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x08' function='0x0'/>
</controller>
<controller type='pci' index='0' model='pcie-root'>
<alias name='pcie.0'/>
</controller>
<controller type='pci' index='1' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='1' port='0x8'/>
<alias name='pci.1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/>
</controller>
<controller type='pci' index='2' model='pcie-to-pci-bridge'>
<model name='pcie-pci-bridge'/>
<alias name='pci.2'/>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</controller>
<controller type='pci' index='3' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='3' port='0x9'/>
<alias name='pci.3'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
</controller>
<controller type='pci' index='4' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='4' port='0xa'/>
<alias name='pci.4'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
</controller>
<controller type='pci' index='5' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='5' port='0xb'/>
<alias name='pci.5'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x3'/>
</controller>
<controller type='pci' index='6' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='6' port='0xc'/>
<alias name='pci.6'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x4'/>
</controller>
<controller type='pci' index='7' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='7' port='0xd'/>
<alias name='pci.7'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x5'/>
</controller>
<controller type='virtio-serial' index='0'>
<alias name='virtio-serial0'/>
<address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
</controller>
<interface type='bridge'>
<mac address='52:54:00:51:5e:71'/>
<source bridge='br0'/>
<target dev='vnet13'/>
<model type='virtio'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
</interface>
<serial type='pty'>
<source path='/dev/pts/0'/>
<target type='isa-serial' port='0'>
<model name='isa-serial'/>
</target>
<alias name='serial0'/>
</serial>
<console type='pty' tty='/dev/pts/0'>
<source path='/dev/pts/0'/>
<target type='serial' port='0'/>
<alias name='serial0'/>
</console>
<channel type='unix'>
<source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-15-Windows 11/org.qemu.guest_agent.0'/>
<target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
<alias name='channel0'/>
<address type='virtio-serial' controller='0' bus='0' port='1'/>
</channel>
<input type='mouse' bus='ps2'>
<alias name='input0'/>
</input>
<input type='keyboard' bus='ps2'>
<alias name='input1'/>
</input>
<tpm model='tpm-tis'>
<backend type='emulator' version='2.0' persistent_state='yes'/>
<alias name='tpm0'/>
</tpm>
<audio id='1' type='none'/>
<hostdev mode='subsystem' type='pci' managed='yes'>
<driver name='vfio'/>
<source>
<address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</source>
<alias name='hostdev0'/>
<rom file='/mnt/cache/appdata/VM/bios-dump/amd_radeon_rx_550_Lexa.rom'/>
<address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0' multifunction='on'/>
</hostdev>
<hostdev mode='subsystem' type='pci' managed='yes'>
<driver name='vfio'/>
<source>
<address domain='0x0000' bus='0x01' slot='0x00' function='0x1'/>
</source>
<alias name='hostdev1'/>
<address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x1'/>
</hostdev>
<hostdev mode='subsystem' type='usb' managed='no'>
<source startupPolicy='optional'>
<vendor id='0x046d'/>
<product id='0xc52b'/>
<address bus='1' device='10'/>
</source>
<alias name='hostdev2'/>
<address type='usb' bus='0' port='1'/>
</hostdev>
<memballoon model='none'/>
</devices>
<seclabel type='dynamic' model='dac' relabel='yes'>
<label>+0:+100</label>
<imagelabel>+0:+100</imagelabel>
</seclabel>
</domain>
Not sure how to fix this, but i would really like to give more cores to the VM.
If anybody finds a solution, please reply.