VirtioFS slow file transfer speeds

[johnsanc314]

I am not sure if I have something misconfigured or if this is just expected behavior, but I am getting poor file transfer performance. Speeds are 45-60 MB/s whereas samba is around 275 MB/s with my setup. Large directory listings with virtiofs are much faster than samba however. Are these speeds expected? If not, is there anything I can do to improve performance?

To Reproduce
Transfer a single large file (~2 GB+) to or from the host OS using the mounted virtiofs drive.

Expected behavior
Speeds should ideally be comparable to samba

Host:

• Distro: Unraid 6.12.6
• Kernel version: Linux 6.1.64-Unraid x86_64
• QEMU version: 7.2.0
• libvirt version: 8.7.0

VM:

• Windows 11
• VirtioFS, 01/10/2024,100.6.101.58000

The VM XML file is pretty standard per the documentation I could find, noteworthy points below:

<?xml version='1.0' encoding='UTF-8'?>
<domain type='kvm' id='9'>
  <name>Windows 11</name>
  <uuid>2b7d02e7-ce93-6934-5afb-641e9b93ab6e</uuid>
  <metadata>
    <vmtemplate xmlns="unraid" name="Windows 11" icon="windows11.png" os="windows11"/>
  </metadata>
  <memory unit='KiB'>41943040</memory>
  <currentMemory unit='KiB'>41943040</currentMemory>
  <memoryBacking>
    <nosharepages/>
    <source type='memfd'/>
    <access mode='shared'/>
  </memoryBacking>
  <vcpu placement='static'>16</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='1'/>
    <vcpupin vcpu='1' cpuset='13'/>
    <vcpupin vcpu='2' cpuset='2'/>
    <vcpupin vcpu='3' cpuset='14'/>
    <vcpupin vcpu='4' cpuset='3'/>
    <vcpupin vcpu='5' cpuset='15'/>
    <vcpupin vcpu='6' cpuset='4'/>
    <vcpupin vcpu='7' cpuset='16'/>
    <vcpupin vcpu='8' cpuset='5'/>
    <vcpupin vcpu='9' cpuset='17'/>
    <vcpupin vcpu='10' cpuset='6'/>
    <vcpupin vcpu='11' cpuset='18'/>
    <vcpupin vcpu='12' cpuset='7'/>
    <vcpupin vcpu='13' cpuset='19'/>
    <vcpupin vcpu='14' cpuset='8'/>
    <vcpupin vcpu='15' cpuset='20'/>
  </cputune>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-q35-7.1'>hvm</type>
    <loader readonly='yes' type='pflash'>/usr/share/qemu/ovmf-x64/OVMF_CODE-pure-efi-tpm.fd</loader>
    <nvram>/etc/libvirt/qemu/nvram/2b7d02e7-ce93-6934-5afb-641e9b93ab6e_VARS-pure-efi-tpm.fd</nvram>
  </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='8' threads='2'/>
    <cache mode='passthrough'/>
    <feature policy='require' name='topoext'/>
  </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='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/domains/iso/Win11_22H2_English_x64v2.iso' index='2'/>
      <backingStore/>
      <target dev='hda' bus='sata'/>
      <readonly/>
      <boot order='2'/>
      <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/user/domains/iso/virtio-win-0.1.240.iso' index='1'/>
      <backingStore/>
      <target dev='hdb' bus='sata'/>
      <readonly/>
      <alias name='sata0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
    <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-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='2' port='0x9'/>
      <alias name='pci.2'/>
      <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'/>
      <alias name='pci.3'/>
      <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'/>
      <alias name='pci.4'/>
      <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'/>
      <alias name='pci.5'/>
      <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'/>
      <alias name='pci.6'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x5'/>
    </controller>
    <controller type='pci' index='7' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='7' port='0xe'/>
      <alias name='pci.7'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x6'/>
    </controller>
    <controller type='pci' index='8' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='8' port='0xf'/>
      <alias name='pci.8'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x7'/>
    </controller>
    <controller type='pci' index='9' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='9' port='0x10'/>
      <alias name='pci.9'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <alias name='virtio-serial0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x00' 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='usb' index='0' model='qemu-xhci' ports='15'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </controller>
    <filesystem type='mount' accessmode='passthrough'>
      <driver type='virtiofs' queue='1024'/>
      <binary path='/usr/libexec/virtiofsd' xattr='on'>
        <cache mode='always'/>
        <sandbox mode='chroot'/>
      </binary>
      <source dir='/mnt/user/Games'/>
      <target dir='Games'/>
      <alias name='fs0'/>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
    </filesystem>
    <interface type='bridge'>
      <mac address='52:54:00:1f:a0:a3'/>
      <source bridge='br0'/>
      <target dev='vnet8'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/1'/>
      <target type='isa-serial' port='0'>
        <model name='isa-serial'/>
      </target>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/1'>
      <source path='/dev/pts/1'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-9-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='0x33' slot='0x00' function='0x0'/>
      </source>
      <alias name='hostdev0'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x33' slot='0x00' function='0x1'/>
      </source>
      <alias name='hostdev1'/>
      <address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x2f' slot='0x00' function='0x1'/>
      </source>
      <alias name='hostdev2'/>
      <address type='pci' domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x32' slot='0x00' function='0x0'/>
      </source>
      <boot order='1'/>
      <alias name='hostdev3'/>
      <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x33' slot='0x00' function='0x2'/>
      </source>
      <alias name='hostdev4'/>
      <address type='pci' domain='0x0000' bus='0x08' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x33' slot='0x00' function='0x3'/>
      </source>
      <alias name='hostdev5'/>
      <address type='pci' domain='0x0000' bus='0x09' slot='0x00' function='0x0'/>
    </hostdev>
    <memballoon model='none'/>
  </devices>
  <seclabel type='dynamic' model='dac' relabel='yes'>
    <label>+0:+100</label>
    <imagelabel>+0:+100</imagelabel>
  </seclabel>
</domain>

[mackid1993]

I can confirm, NVME transfers over VirtioFS run about 400 MB/s. Identical transfers in the same environment over SMB 3-5 GB/s. This is on Unraid QEMU 7.2 with the test VirtioFS drivers. @johnsanc314 also tested the latest Rust virtiofsd with similar results.

[YanVugenfirer]

Hi All,

This is a known issue: https://issues.redhat.com/browse/RHEL-1212

virtio-fs Windows driver implementation was not optimized for performance