15% overhead cpu usage in windows passthrough

Operating Systems & Open Source Linux
, ,
1

Hi,

it seems that I have a 15% overhead in cpu usage between the vm and the host.

<domain type='kvm' id='3'>
  <name>win10</name>
  <uuid>9af2f26c-ac69-4e47-9962-a1cee28a6d59</uuid>
  <memory unit='KiB'>12587008</memory>
  <currentMemory unit='KiB'>12587008</currentMemory>
  <vcpu placement='static'>8</vcpu>
  <cputune>
    <emulatorpin cpuset='0-3'/>
  </cputune>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-q35-2.11'>hvm</type>
    <loader readonly='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.fd</loader>
    <nvram>/var/lib/libvirt/qemu/nvram/win10_VARS.fd</nvram>
    <bootmenu enable='yes'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <hyperv>
      <relaxed state='on'/>
      <vapic state='on'/>
      <spinlocks state='on' retries='8191'/>
      <vendor_id state='on' value='1234567879ab'/>
    </hyperv>
    <kvm>
      <hidden state='on'/>
    </kvm>
    <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-kvm</emulator>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <backingStore/>
      <target dev='sda' 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'>
      <target dev='sdb' bus='sata'/>
      <readonly/>
      <boot order='2'/>
      <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='none' io='native'/>
      <source dev='/dev/sdc'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x08' slot='0x00' function='0x0'/>
    </disk>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native'/>
      <source dev='/dev/sdd'/>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x09' slot='0x00' function='0x0'/>
    </disk>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native'/>
      <source dev='/dev/sde'/>
      <backingStore/>
      <target dev='vdc' bus='virtio'/>
      <alias name='virtio-disk2'/>
      <address type='pci' domain='0x0000' bus='0x0b' slot='0x00' function='0x0'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <alias name='usb'/>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <alias name='usb'/>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <alias name='usb'/>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x2'/>
    </controller>
    <controller type='usb' index='1' model='ich9-ehci1'>
      <alias name='usb1'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x7'/>
    </controller>
    <controller type='sata' index='0'>
      <alias name='ide'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pcie-root'>
      <alias name='pcie.0'/>
    </controller>
    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
      <model name='i82801b11-bridge'/>
      <alias name='pci.1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1e' function='0x0'/>
    </controller>
    <controller type='pci' index='2' model='pci-bridge'>
      <model name='pci-bridge'/>
      <target chassisNr='2'/>
      <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='0x10'/>
      <alias name='pci.3'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0' multifunction='on'/>
    </controller>
    <controller type='pci' index='4' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='4' port='0x11'/>
      <alias name='pci.4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x1'/>
    </controller>
    <controller type='pci' index='5' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='5' port='0x12'/>
      <alias name='pci.5'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x2'/>
    </controller>
    <controller type='pci' index='6' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='6' port='0x13'/>
      <alias name='pci.6'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x3'/>
    </controller>
    <controller type='pci' index='7' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='7' port='0x8'/>
      <alias name='pci.7'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/>
    </controller>
    <controller type='pci' index='8' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='8' port='0x9'/>
      <alias name='pci.8'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <controller type='pci' index='9' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='9' port='0xa'/>
      <alias name='pci.9'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='pci' index='10' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='10' port='0xb'/>
      <alias name='pci.10'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x3'/>
    </controller>
    <controller type='pci' index='11' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='11' port='0xc'/>
      <alias name='pci.11'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x4'/>
    </controller>
    <controller type='pci' index='12' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='12' port='0xd'/>
      <alias name='pci.12'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x5'/>
    </controller>
    <controller type='pci' index='13' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='13' port='0xe'/>
      <alias name='pci.13'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x6'/>
    </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='direct'>
      <mac address='52:54:00:35:c4:20'/>
      <source dev='enp0s31f6' mode='bridge'/>
      <target dev='macvtap1'/>
      <model type='rtl8139'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
    </interface>
    <interface type='network'>
      <mac address='52:54:00:cf:29:b1'/>
      <source network='internal' bridge='virbr2'/>
      <target dev='vnet2'/>
      <model type='virtio'/>
      <alias name='net1'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/2'/>
      <target type='isa-serial' port='0'>
        <model name='isa-serial'/>
      </target>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/2'>
      <source path='/dev/pts/2'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <channel type='spicevmc'>
      <target type='virtio' name='com.redhat.spice.0' state='disconnected'/>
      <alias name='channel0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>
    <input type='tablet' bus='usb'>
      <alias name='input0'/>
      <address type='usb' bus='0' port='2'/>
    </input>
    <input type='mouse' bus='ps2'>
      <alias name='input1'/>
    </input>
    <input type='keyboard' bus='ps2'>
      <alias name='input2'/>
    </input>
    <sound model='ich9'>
      <alias name='sound0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1b' function='0x0'/>
    </sound>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
      </source>
      <alias name='hostdev0'/>
      <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='0x01' slot='0x00' function='0x1'/>
      </source>
      <alias name='hostdev1'/>
      <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x1038'/>
        <product id='0x1600'/>
        <address bus='1' device='14'/>
      </source>
      <alias name='hostdev2'/>
      <address type='usb' bus='0' port='1'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x1038'/>
        <product id='0x1710'/>
        <address bus='1' device='5'/>
      </source>
      <alias name='hostdev3'/>
      <address type='usb' bus='0' port='5'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
      </source>
      <boot order='3'/>
      <alias name='hostdev4'/>
      <address type='pci' domain='0x0000' bus='0x0a' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
      </source>
      <alias name='hostdev5'/>
      <address type='pci' domain='0x0000' bus='0x0c' slot='0x00' function='0x0'/>
    </hostdev>
    <redirdev bus='usb' type='spicevmc'>
      <alias name='redir0'/>
      <address type='usb' bus='0' port='3'/>
    </redirdev>
    <redirdev bus='usb' type='spicevmc'>
      <alias name='redir1'/>
      <address type='usb' bus='0' port='4'/>
    </redirdev>
    <memballoon model='virtio'>
      <stats period='5'/>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
    </memballoon>
  </devices>
  <seclabel type='dynamic' model='selinux' relabel='yes'>
    <label>system_u:system_r:svirt_t:s0:c732,c885</label>
    <imagelabel>system_u:object_r:svirt_image_t:s0:c732,c885</imagelabel>
  </seclabel>
  <seclabel type='dynamic' model='dac' relabel='yes'>
    <label>+107:+107</label>
    <imagelabel>+107:+107</imagelabel>
  </seclabel>
</domain>

The host is a fedora 28 workstation
guest windows 10 pro

When the guest has 3% usage
the host got 20% usgae and it’s causing by the VM according to htop.

hardware: i7-7700k
16G
970 nvidia gtx

What could cause this? or is this normal to have that much overhead?

2

Make sure you are using paravirtualized devices and drivers on the guest like virtio.

Edit oh I see you are.

3

if I forgot something or if I have activated an option I shouldn’t have, any lead can be interesting so don’t hesitate because I’m out of ideas here.

4

I’ve tried those changes:

> <domain type='kvm'>
>   <name>win10</name>
>   <uuid>9af2f26c-ac69-4e47-9962-a1cee28a6d59</uuid>
>   <memory unit='KiB'>12587008</memory>
>   <currentMemory unit='KiB'>12587008</currentMemory>
>   <vcpu>8</vcpu>
>   <cpu mode='host-passthrough'/>
>   <os>
>     <type arch='x86_64' machine='pc-q35-2.11'>hvm</type>
>     <loader readonly='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.fd</loader>
>     <nvram>/var/lib/libvirt/qemu/nvram/win10_VARS.fd</nvram>
>     <bootmenu enable='yes'/>
>   </os>
>   <features>
>     <acpi/>
>     <apic/>
>     <hyperv>
>       <relaxed state='on'/>
>       <vapic state='on'/>
>       <spinlocks state='on' retries='8191'/>
>       <vendor_id state='on' value='1234567879ab'/>
>     </hyperv>
>     <kvm>
>       <hidden state='on'/>
>     </kvm>
>     <vmport state='off'/>
>   </features>
>   <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-kvm</emulator>
>     <disk type='file' device='cdrom'>
>       <driver name='qemu' type='raw'/>
>       <target dev='sda' bus='sata'/>
>       <readonly/>
>       <boot order='1'/>
>       <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>     </disk>
>     <disk type='file' device='cdrom'>
>       <driver name='qemu' type='raw'/>
>       <target dev='sdb' bus='sata'/>
>       <readonly/>
>       <boot order='2'/>
>       <address type='drive' controller='0' bus='0' target='0' unit='1'/>
>     </disk>
>     <disk type='block' device='disk'>
>       <driver name='qemu' type='raw' cache='none' io='native'/>
>       <source dev='/dev/sdc'/>
>       <target dev='vda' bus='virtio'/>
>       <address type='pci' domain='0x0000' bus='0x08' slot='0x00' function='0x0'/>
>     </disk>
>     <disk type='block' device='disk'>
>       <driver name='qemu' type='raw' cache='none' io='native'/>
>       <source dev='/dev/sdd'/>
>       <target dev='vdb' bus='virtio'/>
>       <address type='pci' domain='0x0000' bus='0x09' slot='0x00' function='0x0'/>
>     </disk>
>     <disk type='block' device='disk'>
>       <driver name='qemu' type='raw' cache='none' io='native'/>
>       <source dev='/dev/sde'/>
>       <target dev='vdc' bus='virtio'/>
>       <address type='pci' domain='0x0000' bus='0x0b' slot='0x00' function='0x0'/>
>     </disk>
>     <controller type='usb' index='0' model='ich9-ehci1'>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x7'/>
>     </controller>
>     <controller type='usb' index='0' model='ich9-uhci1'>
>       <master startport='0'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x0' multifunction='on'/>
>     </controller>
>     <controller type='usb' index='0' model='ich9-uhci2'>
>       <master startport='2'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x1'/>
>     </controller>
>     <controller type='usb' index='0' model='ich9-uhci3'>
>       <master startport='4'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x2'/>
>     </controller>
>     <controller type='usb' index='1' model='ich9-ehci1'>
>       <address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x7'/>
>     </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='dmi-to-pci-bridge'>
>       <model name='i82801b11-bridge'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x1e' function='0x0'/>
>     </controller>
>     <controller type='pci' index='2' model='pci-bridge'>
>       <model name='pci-bridge'/>
>       <target chassisNr='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='0x10'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0' multifunction='on'/>
>     </controller>
>     <controller type='pci' index='4' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='4' port='0x11'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x1'/>
>     </controller>
>     <controller type='pci' index='5' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='5' port='0x12'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x2'/>
>     </controller>
>     <controller type='pci' index='6' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='6' port='0x13'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x3'/>
>     </controller>
>     <controller type='pci' index='7' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='7' port='0x8'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/>
>     </controller>
>     <controller type='pci' index='8' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='8' port='0x9'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
>     </controller>
>     <controller type='pci' index='9' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='9' port='0xa'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
>     </controller>
>     <controller type='pci' index='10' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='10' port='0xb'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x3'/>
>     </controller>
>     <controller type='pci' index='11' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='11' port='0xc'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x4'/>
>     </controller>
>     <controller type='pci' index='12' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='12' port='0xd'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x5'/>
>     </controller>
>     <controller type='pci' index='13' model='pcie-root-port'>
>       <model name='pcie-root-port'/>
>       <target chassis='13' port='0xe'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x6'/>
>     </controller>
>     <controller type='virtio-serial' index='0'>
>       <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
>     </controller>
>     <interface type='direct'>
>       <mac address='52:54:00:35:c4:20'/>
>       <source dev='enp0s31f6' mode='bridge'/>
>       <model type='rtl8139'/>
>       <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
>     </interface>
>     <interface type='network'>
>       <mac address='52:54:00:cf:29:b1'/>
>       <source network='internal'/>
>       <model type='virtio'/>
>       <address type='pci' domain='0x0000' bus='0x04' 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='0x01' slot='0x00' function='0x0'/>
>       </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='0x01' slot='0x00' function='0x1'/>
>       </source>
>       <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
>     </hostdev>
>     <hostdev mode='subsystem' type='usb' managed='yes'>
>       <source>
>         <vendor id='0x1038'/>
>         <product id='0x1600'/>
>       </source>
>       <address type='usb' bus='0' port='1'/>
>     </hostdev>
>     <hostdev mode='subsystem' type='usb' managed='yes'>
>       <source>
>         <vendor id='0x1038'/>
>         <product id='0x1710'/>
>       </source>
>       <address type='usb' bus='0' port='5'/>
>     </hostdev>
>     <hostdev mode='subsystem' type='pci' managed='yes'>
>       <source>
>         <address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
>       </source>
>       <boot order='3'/>
>       <address type='pci' domain='0x0000' bus='0x0a' 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='0x0c' slot='0x00' function='0x0'/>
>     </hostdev>
>     <redirdev bus='usb' type='spicevmc'>
>       <address type='usb' bus='0' port='3'/>
>     </redirdev>
>     <redirdev bus='usb' type='spicevmc'>
>       <address type='usb' bus='0' port='4'/>
>     </redirdev>
>     <memballoon model='virtio'>
>       <address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
>     </memballoon>
>   </devices>
> </domain>

as yopu can see I4ve put the host-passthrough parameters but the vm doesn’t detect the whole cores but only 2… Why is that?

5

why have I to do this to actually have the good topology?
And in the peripherals it detects the good cpu and even the good amount of cores if I don’t do this, but the system only acknowledge 2 Cpu on 2 sockets if I don’t.

  <cpu mode='host-passthrough'>
   <topology sockets='1' cores='4' threads='2'/>
  </cpu>

and I still have this fucking overhead.
should the network card also be virtio?

6

for an example, in GTA V for the testing, in a stopped car in online session, I do around 55% cpu activity in win10 guest. But for the host at the same time I have around 71% activity and everything with this VM. a piece of hardware needs translation here or the guest cpu is not well configured in the VM I don’t know but there is clearly a problem no?

7

As the diagnostic in the reddit thread vfio is quite the same, the vm has a lot of kvm_entry and kvm_exit

but also a lot of kvm_apic and others.

here is my xml:

https://pastebin.com/qPmqesmL

my host system is a fedora 28 workstation on a i7-7700k.

the system drive for this windows is an actual nvme drive that I passtrhough with the pci controller

the other drives are actual physical hdds. Maybe I shouldn’t do that or that’s why there is the overhead?

here is several results of ‘sudo perf stat -e ‘kvm:*’ -a – sleep 1’

https://pastebin.com/Ujdn8ZRh

the solution posted here: https://www.reddit.com/r/VFIO/comments/80p1q7/high_kvmqemu_cpu_utilization_when_windows_10/ didn’t help

Used clean, freshly installed Windows 10 with up to date drives and no additional software

Tried installing guest KVM drivers. This actually made things slightly worse.

Tried disabling every unused device inside a VM, or even optional devices like networking card, usb headset, emulated sata cd drive and sata controller

Googled the hell out of the internet

didn’t try:

  • setting options kvm halt_poll_ns=0to /etc/modprobe.d/kvm.conf

  • another server because I read that with host-passthrough, you shouldn’t do that.

  • no other kernel tried besides the updates from the kernel I started with 2 months ago. presently, it’s 4.17.17.

for the command line 'sudo perf kvm --host top -p ‘pidof qemu’ I don’t know which one to choose in htop because I have several ones for the same vm. But I have watch some of the pid cocnerned by this process and it’s mostly around 65% of vmx_vcpu_run happening in kernel.

5% with read_tsc in kernek too and if I move my mouse a lot, 5% of vmx_interrupt_allowed in kernel too.

my /etc/modprobe.d/kvm.conf is like that at the moment:

options kvm_intel nested=1

options kvm-intel enable-shadow_vmcs=1

options kvm-intel enable_apicv=1

options kvm_intel ept=1

#options kvm_amd nested=1



options vfio-pci ids=10de:13c2,10de:0fbb

I had to specify my topology because if not, the system task manager of windows would only acknowledge 2 cpu on 2 sockets while in the device manager it would recognize my whole cpu…

So my question is how do I delete the overhead of ~15% of cpu ? which is the equivalent of one complete thread?

is it because of the usb and so should I buy a complete usb card?

is it because of the system drive is a nvme and so I had to add the pci controller to the vm?

is it because of my kvm.conf where I enabled nested virt and some other stuff?

or is it because of something bad happening with the vcpu ?