I'm running a QEMU/KVM virtual machine on Debian 13, following the OVMF tutorial on the Arch Wiki ([https://wiki.archlinux.org/title/PCI\_passthrough\_via\_OVMF](https://wiki.archlinux.org/title/PCI_passthrough_via_OVMF)).

Running i3-7350k, 16G DDR4, RX 580, all on a Gigabyte B250M-DS3H.

My setup is mostly successful - PCI passthrough with the RX 580 works flawlessly; both CPU and GPU benchmarks yield basically native results. It's all great for now, save for this one issue. I get absolutely abhorrent stutters in games, and I assume this is the reason.

I have tried using hugepages - both 2M transparent hugepages, and static 1G - to no avail. As you will see below, I also configured CPU pinning and cache passthrough. I looked around the internet and couldn't find someone with a similar problem... so here I am. The only thing I can think of is something being wrong with emulated chipset, the Q35?

Here is the full XML config of my VM, if anyone has an idea what might the issue be:

    <domain type="kvm">
      <name>win10-15022026</name>
      <uuid>35a6f1ca-6246-4f23-895d-954397767a2a</uuid>
      <metadata>
        <libosinfo:libosinfo xmlns:libosinfo="http://libosinfo.org/xmlns/libvirt/domain/1.0">
          <libosinfo:os id="http://microsoft.com/win/10"/>
        </libosinfo:libosinfo>
      </metadata>
      <memory unit="KiB">10485760</memory>
      <currentMemory unit="KiB">10485760</currentMemory>
      <vcpu placement="static">4</vcpu>
      <cputune>
        <vcpupin vcpu="0" cpuset="1"/>
        <vcpupin vcpu="1" cpuset="3"/>
        <vcpupin vcpu="2" cpuset="0"/>
        <vcpupin vcpu="3" cpuset="2"/>
        <emulatorpin cpuset="0"/>
      </cputune>
      <os firmware="efi">
        <type arch="x86_64" machine="pc-q35-10.0">hvm</type>
        <firmware>
          <feature enabled="no" name="enrolled-keys"/>
          <feature enabled="no" name="secure-boot"/>
        </firmware>
        <loader readonly="yes" type="pflash" format="raw">/usr/share/OVMF/OVMF_CODE_4M.fd</loader>
        <nvram template="/usr/share/OVMF/OVMF_VARS_4M.fd" templateFormat="raw" format="raw">/var/lib/libvirt/qemu/nvram/win10-15022026_VARS.fd</nvram>
        <boot dev="hd"/>
        <bootmenu enable="yes"/>
      </os>
      <features>
        <acpi/>
        <apic/>
        <hyperv mode="custom">
          <relaxed state="on"/>
          <vapic state="on"/>
          <spinlocks state="on" retries="8191"/>
          <vpindex state="on"/>
          <runtime state="on"/>
          <synic state="on"/>
          <stimer state="on"/>
          <vendor_id state="on" value="randomid"/>
          <frequencies state="on"/>
          <tlbflush state="on"/>
          <ipi state="on"/>
          <evmcs state="on"/>
          <avic state="on"/>
        </hyperv>
        <vmport state="off"/>
      </features>
      <cpu mode="host-passthrough" check="none" migratable="on">
        <topology sockets="1" dies="1" clusters="1" cores="2" threads="2"/>
        <cache mode="passthrough"/>
      </cpu>
      <clock offset="localtime">
        <timer name="rtc" tickpolicy="catchup"/>
        <timer name="pit" tickpolicy="delay"/>
        <timer name="hpet" present="no"/>
        <timer name="hypervclock" present="yes"/>
      </clock>
      <on_poweroff>destroy</on_poweroff>
      <on_reboot>restart</on_reboot>
      <on_crash>destroy</on_crash>
      <pm>
        <suspend-to-mem enabled="no"/>
        <suspend-to-disk enabled="no"/>
      </pm>
      <devices>
        <emulator>/usr/bin/qemu-system-x86_64</emulator>
        <disk type="file" device="disk">
          <driver name="qemu" type="qcow2"/>
          <source file="/var/lib/libvirt/images/pool-windwos/win-28022026.qcow2"/>
          <target dev="sda" bus="scsi"/>
          <address type="drive" controller="0" bus="0" target="0" unit="0"/>
        </disk>
        <controller type="usb" index="0" model="qemu-xhci" ports="15">
          <address type="pci" domain="0x0000" bus="0x02" slot="0x00" function="0x0"/>
        </controller>
        <controller type="pci" index="0" model="pcie-root"/>
        <controller type="pci" index="1" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="1" port="0x10"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x0" multifunction="on"/>
        </controller>
        <controller type="pci" index="2" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="2" port="0x11"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x1"/>
        </controller>
        <controller type="pci" index="3" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="3" port="0x12"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x2"/>
        </controller>
        <controller type="pci" index="4" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="4" port="0x13"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x3"/>
        </controller>
        <controller type="pci" index="5" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="5" port="0x14"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x4"/>
        </controller>
        <controller type="pci" index="6" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="6" port="0x15"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x5"/>
        </controller>
        <controller type="pci" index="7" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="7" port="0x16"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x6"/>
        </controller>
        <controller type="pci" index="8" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="8" port="0x17"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x7"/>
        </controller>
        <controller type="pci" index="9" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="9" port="0x18"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x0" multifunction="on"/>
        </controller>
        <controller type="pci" index="10" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="10" port="0x19"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x1"/>
        </controller>
        <controller type="pci" index="11" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="11" port="0x1a"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x2"/>
        </controller>
        <controller type="pci" index="12" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="12" port="0x1b"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x3"/>
        </controller>
        <controller type="pci" index="13" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="13" port="0x1c"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x4"/>
        </controller>
        <controller type="pci" index="14" model="pcie-root-port">
          <model name="pcie-root-port"/>
          <target chassis="14" port="0x1d"/>
          <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x5"/>
        </controller>
        <controller type="scsi" index="0" model="virtio-scsi">
          <address type="pci" domain="0x0000" bus="0x03" slot="0x00" function="0x0"/>
        </controller>
        <controller type="sata" index="0">
          <address type="pci" domain="0x0000" bus="0x00" slot="0x1f" function="0x2"/>
        </controller>
        <controller type="virtio-serial" index="0">
          <address type="pci" domain="0x0000" bus="0x04" slot="0x00" function="0x0"/>
        </controller>
        <interface type="network">
          <mac address="52:54:00:6a:a7:9b"/>
          <source network="default"/>
          <model type="e1000e"/>
          <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>
        </interface>
        <serial type="pty">
          <target type="isa-serial" port="0">
            <model name="isa-serial"/>
          </target>
        </serial>
        <console type="pty">
          <target type="serial" port="0"/>
        </console>
        <input type="evdev">
          <source dev="/dev/input/by-id/usb-Lite-On_Technology_USB_Productivity_Option_Keyboard__has_the_hub_in_#_1__-event-kbd" grab="all" grabToggle="scrolllock" repeat="on"/>
        </input>
        <input type="evdev">
          <source dev="/dev/input/by-id/usb-Logitech_USB_Optical_Mouse-event-mouse"/>
        </input>
        <input type="mouse" bus="virtio">
          <address type="pci" domain="0x0000" bus="0x06" slot="0x00" function="0x0"/>
        </input>
        <input type="keyboard" bus="virtio">
          <address type="pci" domain="0x0000" bus="0x07" slot="0x00" function="0x0"/>
        </input>
        <input type="mouse" bus="ps2"/>
        <input type="keyboard" bus="ps2"/>
        <sound model="ich9">
          <address type="pci" domain="0x0000" bus="0x00" slot="0x1b" function="0x0"/>
        </sound>
        <audio id="1" type="none"/>
        <hostdev mode="subsystem" type="pci" managed="yes">
          <source>
            <address domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>
          </source>
          <address type="pci" domain="0x0000" bus="0x08" slot="0x00" function="0x0"/>
        </hostdev>
        <hostdev mode="subsystem" type="pci" managed="yes">
          <source>
            <address domain="0x0000" bus="0x01" slot="0x00" function="0x1"/>
          </source>
          <address type="pci" domain="0x0000" bus="0x09" slot="0x00" function="0x0"/>
        </hostdev>
        <watchdog model="itco" action="reset"/>
        <memballoon model="virtio">
          <address type="pci" domain="0x0000" bus="0x05" slot="0x00" function="0x0"/>
        </memballoon>
      </devices>
    </domain>

Extremely low memory speed, heavy stutters in games