RX 5700XT VFIO Passthrough - CPU Bottleneck?

Hi folks!

Looking for your advice/opinions please.

I’ve been successfully running a Windows 10 VM with my 290x passed-through for a while now. Recently I upgraded my beloved 290x to a 5700XT. I applied the Navi Reset Patch to my kernel, everything worked… Happy days! :smiley: .

However I’ve been playing Borderlands 3 for about a week now and have been feeling like performance should be better. I’ve been achieving an average of 70fps on Ultra settings. Which is absolutely playable, just felt like it could/should be better.

In an effort to gain some performance. I updated my BIOS and moved the 5700XT from an PCI-E x8 to a PCI-E x16 slot. This actually made performance worse! Pretty sure this was because the BIOS update wiped my overclock settings (4.6Ghz). So I overclocked again, but can only achieve 4.5Ghz now at reasonable temps :cry: Must be because the GPU is closer to the CPU cooler and hindering airflow? At this point Borerlands 3 was down to 65fps.

So I thought I’d try booting up Windows on bare metal and the difference was pretty drastic. An average of 115fps.

I’m pretty confident that my CPU (i7 6700k) is bottle-necking the GPU in a VFIO configuration. I know there are overheads with virtualisation, but difference in gaming performance is considerable here.

This is all a long winded way of asking. Is my CPU a bottleneck in this configuration?

Sadly I get the feeling that I’m back to Dual Booting until I can afford a new Mobo and CPU. CPU upgrade paths seem limited by the socket. Deeply regretting not getting an AM4 board now :disappointed:

Hardware

CPU Intel i7 6700k
Motherboard Asus Maximus VIII Hero Z170
RAM 32GB Corsair Vengence @ 3000Mhz
GPU (Host) Radeon R5 230
GPU (Guest) Radeon RX 5700XT

VFIO Config

<domain type="kvm">
  <name>win10-q35</name>
  <uuid>13986d16-2a9f-4bf4-a24a-661f07e99300</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">16777216</memory>
  <currentMemory unit="KiB">16777216</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <vcpu placement="static" current="6">8</vcpu>
  <iothreads>1</iothreads>
  <cputune>
    <vcpupin vcpu="0" cpuset="1"/>
    <vcpupin vcpu="1" cpuset="2"/>
    <vcpupin vcpu="2" cpuset="3"/>
    <vcpupin vcpu="3" cpuset="5"/>
    <vcpupin vcpu="4" cpuset="6"/>
    <vcpupin vcpu="5" cpuset="7"/>
    <emulatorpin cpuset="0,4"/>
    <iothreadpin iothread="1" cpuset="0,4"/>
  </cputune>
  <os>
    <type arch="x86_64" machine="pc-q35-4.2">hvm</type>
    <loader readonly="yes" type="pflash">/usr/share/ovmf/x64/OVMF_CODE.fd</loader>
    <nvram>/var/lib/libvirt/qemu/nvram/win10_VARS.fd</nvram>
    <boot dev="hd"/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <hyperv>
      <relaxed state="on"/>
      <vapic state="on"/>
      <spinlocks state="on" retries="8191"/>
    </hyperv>
    <vmport state="off"/>
  </features>
  <cpu mode="host-passthrough" check="none">
    <topology sockets="1" cores="4" threads="2"/>
  </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="block" device="disk">
      <driver name="qemu" type="raw" cache="none" io="native"/>
      <source dev="/dev/disk/by-id/ata-KINGSTON_SH103S3120G_50026B722902764F"/>
      <target dev="sda" bus="scsi"/>
      <address type="drive" controller="0" bus="0" target="0" unit="0"/>
    </disk>
    <disk type="block" device="disk">
      <driver name="qemu" type="raw" cache="none" io="native"/>
      <source dev="/dev/disk/by-id/ata-WDC_WDS500G1B0A-00H9H0_164407800514"/>
      <target dev="sdb" bus="scsi"/>
      <address type="drive" controller="0" bus="0" target="0" unit="1"/>
    </disk>
    <controller type="usb" index="0" model="qemu-xhci" ports="15">
      <address type="pci" domain="0x0000" bus="0x03" slot="0x00" function="0x0"/>
    </controller>
    <controller type="scsi" index="0" model="virtio-scsi">
      <address type="pci" domain="0x0000" bus="0x04" slot="0x00" function="0x0"/>
    </controller>
    <controller type="sata" index="0">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x1f" function="0x2"/>
    </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="0x8"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x0" multifunction="on"/>
    </controller>
    <controller type="pci" index="2" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="2" port="0x9"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x1"/>
    </controller>
    <controller type="pci" index="3" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="3" port="0xa"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x2"/>
    </controller>
    <controller type="pci" index="4" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="4" port="0xb"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x3"/>
    </controller>
    <controller type="pci" index="5" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="5" port="0xc"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x4"/>
    </controller>
    <controller type="pci" index="6" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="6" port="0xd"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x5"/>
    </controller>
    <controller type="pci" index="7" model="pcie-to-pci-bridge">
      <model name="pcie-pci-bridge"/>
      <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>
    </controller>
    <controller type="pci" index="8" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="8" port="0xe"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x6"/>
    </controller>
    <controller type="pci" index="9" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="9" port="0xf"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x7"/>
    </controller>
    <controller type="pci" index="10" model="pcie-root-port">
      <model name="pcie-root-port"/>
      <target chassis="10" port="0x10"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x0"/>
    </controller>
    <interface type="network">
      <mac address="52:54:00:99:d7:89"/>
      <source network="default"/>
      <model type="virtio"/>
      <link state="up"/>
      <address type="pci" domain="0x0000" bus="0x02" slot="0x00" function="0x0"/>
    </interface>
    <input type="mouse" bus="ps2"/>
    <input type="keyboard" bus="ps2"/>
    <hostdev mode="subsystem" type="pci" managed="yes">
      <source>
        <address domain="0x0000" bus="0x00" slot="0x14" function="0x0"/>
      </source>
      <address type="pci" domain="0x0000" bus="0x07" slot="0x01" function="0x0"/>
    </hostdev>
    <hostdev mode="subsystem" type="pci" managed="yes">
      <source>
        <address domain="0x0000" bus="0x03" slot="0x00" function="0x0"/>
      </source>
      <address type="pci" domain="0x0000" bus="0x05" slot="0x00" function="0x0"/>
    </hostdev>
    <hostdev mode="subsystem" type="pci" managed="yes">
      <source>
        <address domain="0x0000" bus="0x03" slot="0x00" function="0x1"/>
      </source>
      <address type="pci" domain="0x0000" bus="0x06" slot="0x00" function="0x0"/>
    </hostdev>
    <hostdev mode="subsystem" type="pci" managed="yes">
      <source>
        <address domain="0x0000" bus="0x05" slot="0x00" function="0x0"/>
      </source>
      <address type="pci" domain="0x0000" bus="0x08" slot="0x00" function="0x0"/>
    </hostdev>
    <memballoon model="virtio">
      <address type="pci" domain="0x0000" bus="0x09" slot="0x00" function="0x0"/>
    </memballoon>
  </devices>
</domain>