i'm wondering about some performance issues. I have some problems with the implementation, but that isn't my current focus. I built a computer for my daughters to both concurrently play minecraft on. To accomplish this, i'm using linux KVM. The guests are using Windows 10.

I did this two ways, 1 using CLI and one using virt-manager.

the CLI version is as follows

qemu-system-x86_64 -enable-kvm -M q35 -m 3072 -cpu host \
-smp 2,sockets=1,cores=2,threads=1 \
-bios /usr/share/qemu/bios.bin -vga none \
-device virtio-scsi-pci,id=scsi \
-drive file=/srv/wip.img,format=raw,id=disk,if=none,cache=none,aio=native \
-device scsi-hd,drive=disk \
-cdrom /home/driz/win10.iso \
-device ioh3420,bus=pcie.0,addr=1c.0,multifunction=on,port=1,chassis=1,id=root.1 \
-device vfio-pci,host=01:00.0,bus=root.1,addr=00.0,multifunction=on,x-vga=on \
-device virtio-net-pci,mac=52:54:00:ea:c8:8d \
-usb -usbdevice host:040b:2000 -usbdevice host:046d:c01e -usbdevice host:0d8c:0014 \
-boot menu=on

we can probably ignore the video card passthrough and usb passthrough for now (unless they are factors). Assuming I properly understand what i did here, i have a virtio scsi controller and a scsi disk attached to it using raw storage. I mount a cd to install windows 10 (i use the qemu window to swap it for the virtio drivers for the disk during install). This installation takes a very long time and disk performance seems poor. The actual windows install takes around 20 minutes.

On the other hand, creating the machine in virt-manager, with what i think are the same settings (below is the command line i grabbed from ps )

qemu-system-x86_64 -enable-kvm -name guest=win10,debug-threads=on -S \
-object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-2-win10/master-key.aes \
-machine pc-q35-2.6,accel=kvm,usb=off \
-cpu host,hv_time,hv_relaxed,hv_vapic,hv_spinlocks=0x1fff \
-drive file=/srv/ovmf-x64/OVMF_CODE-pure-efi.fd,if=pflash,format=raw,unit=0,readonly=on \
-drive file=/var/lib/libvirt/qemu/nvram/win10_VARS.fd,if=pflash,format=raw,unit=1 \
-m 3072 -realtime mlock=off -smp 1,maxcpus=2,sockets=1,cores=1,threads=2 \
-uuid 6529c02d-b03f-4adf-8cbf-58dc9227e976 -no-user-config -nodefaults \
-chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-2-win10/monitor.sock,server,nowait \
-mon chardev=charmonitor,id=monitor,mode=control \
-rtc base=localtime,driftfix=slew \
-global kvm-pit.lost_tick_policy=discard -no-hpet -no-shutdown \
-global ICH9-LPC.disable_s3=1 \
-global ICH9-LPC.disable_s4=1 \
-boot strict=on \
-device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1e \
-device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x0 \
-device ich9-usb-ehci1,id=usb,bus=pcie.0,addr=0x1d.0x7 \
-device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pcie.0,multifunction=on,addr=0x1d \
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pcie.0,addr=0x1d.0x1 \
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pcie.0,addr=0x1d.0x2 \
-device virtio-scsi-pci,id=scsi0,bus=pci.2,addr=0x3 \
-device virtio-serial-pci,id=virtio-serial0,bus=pci.2,addr=0x4 \
-drive file=/srv/wip.img,format=raw,if=none,id=drive-scsi0-0-0-0,cache=none,aio=native \
-device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1 \
-drive file=/srv/win10.iso,format=raw,if=none,media=cdrom,id=drive-sata0-0-1,readonly=on \
-device ide-cd,bus=ide.1,drive=drive-sata0-0-1,id=sata0-0-1 \
-drive file=/srv/virtio-win.iso,format=raw,if=none,media=cdrom,id=drive-sata0-0-2,readonly=on \
-device ide-cd,bus=ide.2,drive=drive-sata0-0-2,id=sata0-0-2 \
-netdev tap,fd=26,id=hostnet0 \
-device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:2b:38:74,bus=pci.2,addr=0x1 -chardev pty,id=charserial0 \
-device isa-serial,chardev=charserial0,id=serial0 \
-chardev spicevmc,id=charchannel0,name=vdagent \
-device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spice.0 \
-device usb-tablet,id=input0,bus=usb.0,port=1 \
-spice port=5900,addr=,disable-ticketing,image-compression=off,seamless-migration=on \
-device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pcie.0,addr=0x1 \
-device intel-hda,id=sound0,bus=pci.2,addr=0x2 \
-device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 \
-chardev spicevmc,id=charredir0,name=usbredir \
-device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 \
-chardev spicevmc,id=charredir1,name=usbredir \
-device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 \
-device virtio-balloon-pci,id=balloon0,bus=pci.2,addr=0x5 \
-msg timestamp=on

windows installs here in about 7 minutes. In both cases, the raw disk image is freshly created using dd, same size and specs. I create it via dd on the command line in both cases (not with virt-manager) My question is, why is the install so much faster using the virt-manager build vs my CLI build. I see that there are some extra controllers in the virt-manager setup, but it really doesn't make sense to me. the major differences I see are the top scenario on the CLI is seabios, the virt-manager build is uefi. What is strange is that during windows boot up, where usually uefi would display the manufacturer's logo, i see the windows logo as if this were a bios boot up. Perhaps this is due to it being virtual, but i expected to see the tiano logo during windows boot since it's uefi.

since the xml from virsh may reveal more information, i've attached it below

<domain type='kvm' id='2'>
  <memory unit='KiB'>3145728</memory>
  <currentMemory unit='KiB'>3145728</currentMemory>
  <vcpu placement='static' current='1'>2</vcpu>
    <type arch='x86_64' machine='pc-q35-2.6'>hvm</type>
    <loader readonly='yes' type='pflash'>/srv/ovmf-x64/OVMF_CODE-pure-efi.fd</loader>
    <boot dev='hd'/>
      <relaxed state='on'/>
      <vapic state='on'/>
      <spinlocks state='on' retries='8191'/>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='1' threads='2'/>
  <clock offset='localtime'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
    <timer name='hypervclock' present='yes'/>
    <suspend-to-mem enabled='no'/>
    <suspend-to-disk enabled='no'/>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native'/>
      <source file='/srv/wip.img'/>
      <target dev='sda' bus='scsi'/>
      <alias name='scsi0-0-0-0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/srv/win10.iso'/>
      <target dev='sdb' bus='sata'/>
      <alias name='sata0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/srv/virtio-win.iso'/>
      <target dev='sdc' bus='sata'/>
      <alias name='sata0-0-2'/>
      <address type='drive' controller='0' bus='0' target='0' unit='2'/>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1d' function='0x7'/>
    <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 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 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 type='scsi' index='0' model='virtio-scsi'>
      <alias name='scsi0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x0'/>
    <controller type='sata' index='0'>
      <alias name='ide'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
    <controller type='pci' index='0' model='pcie-root'>
      <alias name='pcie.0'/>
    <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 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 type='virtio-serial' index='0'>
      <alias name='virtio-serial0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x04' function='0x0'/>
    <interface type='direct'>
      <mac address='52:54:00:2b:38:74'/>
      <source dev='enp0s31f6' mode='bridge'/>
      <target dev='macvtap0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
    <serial type='pty'>
      <source path='/dev/pts/2'/>
      <target port='0'/>
      <alias name='serial0'/>
    <console type='pty' tty='/dev/pts/2'>
      <source path='/dev/pts/2'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    <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'/>
    <input type='tablet' bus='usb'>
      <alias name='input0'/>
      <address type='usb' bus='0' port='1'/>
    <input type='mouse' bus='ps2'>
      <alias name='input1'/>
    <input type='keyboard' bus='ps2'>
      <alias name='input2'/>
    <graphics type='spice' port='5900' autoport='yes' listen=''>
      <listen type='address' address=''/>
      <image compression='off'/>
    <sound model='ich6'>
      <alias name='sound0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x0'/>
      <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
    <redirdev bus='usb' type='spicevmc'>
      <alias name='redir0'/>
      <address type='usb' bus='0' port='2'/>
    <redirdev bus='usb' type='spicevmc'>
      <alias name='redir1'/>
      <address type='usb' bus='0' port='3'/>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x05' function='0x0'/>
  <seclabel type='dynamic' model='apparmor' relabel='yes'>
  <seclabel type='dynamic' model='dac' relabel='yes'>
  • 1
    I'm not sure what the question here is. Naturally QEMU or KVM won't present the bare metal's BIOS as the VM boots up; the hypervisor is presenting its own emulated BIOS. – DopeGhoti Jan 5 '17 at 20:21
  • the question is why one is faster than the other. they are both virtual machines using qemu. one is 32% faster than the other but as far as I can tell (aside from uefi vs bios) they are the same. – driz Jan 5 '17 at 20:31
  • post both xml's. – Aaron Walerstein Mar 23 '17 at 7:44
  • @AaronWalerstein there is one and it is posted, i'm not sure you understood the question. – driz Mar 24 '17 at 13:44
  • You have a different CPU layout from virt-manager, depending on the underlying hardware this can have odd effects (i.e if you specify more cores than actually exist on the underlying machine, qemu is going to try and emulate the effect). You also have different options for your disks - you probably don't want to be using aio=native on what could be a sparse file, for instance. – cbz Jan 14 at 23:49

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