[libvirt-users] Windows Guest I/O performance issues (already using virtio)

[Matt Schumacher]

List,

I have a number of Windows 2016 servers I am deploying, but I’m having some I/O performance issues.  I have done all of the obvious things like virtio drivers, but am finding there is more performance to be found with hyper-v extensions, how we virtualize the hardware clock, and iothreads.  I’m using ZVOLs to back the VM, and I’m using 4k block sizes, which seems to offer the best 4k random read/write performance (mail and database workloads), but maybe I’m missing something at this layer too.

Questions:


  1.  Does my VM config look reasonable for the latest releases of windows?  Are there features I should be using that will help performance?
  2.  Why does the hypervclock timer make so much performance difference in windows VMs?
  3.  Does my virtualized CPU model make sense?  I defined Haswell-noTSX-IBRS and libvirt added the features.
  4.  Which kernel branch offers the best stability and performance?
  5.  Are there performance gains in using UEFI booting the windows guest and defining “<blockio logical_block_size='4096' physical_block_size='4096'/>”?  Perhaps better block size consistency through to the zvol?


Here is my setup:

48 core Haswell CPU
192G Ram
Linux 4.14.61 or 4.9.114 (testing both)
ZFS file system on optane SSD drive or ZFS file system on dumb HBA with 8 spindles of 15k disks (testing both)
4k block size zvol for virtual machines
32G arc cache

Here is my VM:

<domain type='kvm' id='12'>
  <name>testvm</name>
  <memory unit='KiB'>33554432</memory>
  <currentMemory unit='KiB'>33554432</currentMemory>
  <vcpu placement='static'>12</vcpu>
  <iothreads>1</iothreads>
  <os>
    <type arch='x86_64' machine='pc-i440fx-2.12'>hvm</type>
    <boot dev='cdrom'/>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <hyperv>
      <relaxed state='on'/>
      <vapic state='on'/>
      <spinlocks state='on' retries='8191'/>
      <vpindex state='on'/>
      <runtime state='on'/>
      <synic state='on'/>
      <reset state='on'/>
      <vendor_id state='on' value='KVM Hv'/>
    </hyperv>
  </features>
  <cpu mode='custom' match='exact' check='full'>
    <model fallback='forbid'>Haswell-noTSX-IBRS</model>
    <topology sockets='1' cores='6' threads='2'/>
    <feature policy='require' name='vme'/>
    <feature policy='require' name='f16c'/>
    <feature policy='require' name='rdrand'/>
    <feature policy='require' name='hypervisor'/>
    <feature policy='require' name='arat'/>
    <feature policy='disable' name='spec-ctrl'/>
    <feature policy='require' name='xsaveopt'/>
    <feature policy='require' name='abm'/>
  </cpu>
  <clock offset='localtime'>
   <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='yes'/>
    <timer name='hypervclock' present='yes'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native' ioeventfd='on' iothread='1'/>
      <source dev='/dev/zvol/datastore/vm/testvm-vda'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <alias name='ide0-1-0'/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <alias name='ide'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='piix3-uhci'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'>
      <alias name='pci.0'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <alias name='virtio-serial0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </controller>
    <interface type='bridge'>
      <source bridge='lan'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-12-testvm/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='tablet' bus='usb'>
      <alias name='input0'/>
      <address type='usb' bus='0' port='1'/>
    </input>
    <input type='mouse' bus='ps2'>
      <alias name='input1'/>
    </input>
    <input type='keyboard' bus='ps2'>
      <alias name='input2'/>
    </input>
    <graphics type='vnc' port='5901' autoport='no' listen='0.0.0.0'>
      <listen type='address' address='0.0.0.0'/>
    </graphics>
    <video>
      <model type='cirrus' vram='16384' heads='1' primary='yes'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='none'/>
  </devices>
  <seclabel type='dynamic' model='dac' relabel='yes'>
    <label>+0:+100</label>
    <imagelabel>+0:+100</imagelabel>
  </seclabel>
</domain>
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