As the virtio related parts aren't the ones hanging (network and disks still work...) it's unlikely, but it makes a night and day difference.
Removing -no-hpet as suggested does seem to make a difference, too. (Changing the tick policy doesn't, for me.) However, I've found that there are various options which when changed can massively influence the likelihood of hangs - but it's not always the same options for all VMs. With the difference being hangups after 1 to at most 2 migrations with one setting, or the VMs still being alive and kicking after 20 and more migrations with the other. However the options I've tested appear to be unrelated. Eq. in my test setups this happened with VNC settings, CPU types, toggling our backend's ssh tunnel for encryption (which should cause nothing but changes in timing from the perspective of qemu); and of course replacing virtio devices always had this effect in my tests. All this might point to some kind of race condition or time keeping problem, but I can't seem to pinpoint it. Enabling hpet isn't a good option btw., since #599958 [Timedrift problems with Win7: hpet missing time drift fixups] appears to still be an open issue. => https://bugs.launchpad.net/qemu/+bug/599958 (This entry is from 2010 :-( ) -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1618431 Title: windows hangs after live migration with virtio Status in QEMU: New Bug description: Several of our users reported problems with windows machines hanging after live migrations. The common denominator _seems_ to be virtio devices. I've managed to reproduce this reliably on a windows 10 (+ virtio-win-0.1.118) guest, always within 1 to 5 migrations, with a virtio-scsi hard drive and a virtio-net network device. (When I replace the virtio-net device with an e1000 it takes 10 or more migrations, and without virtio devices I have not (yet) been able to reproduce this problem. I also could not reproduce this with a linux guest. Also spice seems to improve the situation, but doesn't solve it completely). I've tested quite a few tags from qemu-git (v2.2.0 through v2.6.1, and 2.6.1 with the patches mentioned on qemu-stable by Peter Lieven) and the behavior is the same everywhere. The reproducibility seems to be somewhat dependent on the host hardware, which makes investigating this issue that much harder. Symptoms: After the migration the windows graphics stack just hangs. Background processes are still running (eg. after installing an ssh server I could still login and get a command prompt after the hang was triggered... not that I'd know what to do with that on a windows machine...) - commands which need no GUI access work, the rest just hangs there on the command line, too. It's also capable of responding to an NMI sent via the qemu monitor: it then seems to "recover" and manages to show the blue sad-face screen that something happened, reboots successfully and is usable again without restarting the qemu process in between. From there whole the process can be repeated. Here's what our command line usually looks like: /usr/bin/qemu -daemonize \ -enable-kvm \ -chardev socket,id=qmp,path=/var/run/qemu-server/101.qmp,server,nowait -mon chardev=qmp,mode=control \ -pidfile /var/run/qemu-server/101.pid \ -smbios type=1,uuid=07fc916e-24c2-4eef-9827-4ab4026501d4 \ -name win10 \ -smp 6,sockets=1,cores=6,maxcpus=6 \ -nodefaults \ -boot menu=on,strict=on,reboot-timeout=1000 \ -vga std \ -vnc unix:/var/run/qemu-server/101.vnc \ -no-hpet \ -cpu kvm64,hv_spinlocks=0x1fff,hv_vapic,hv_time,hv_reset,hv_vpindex,hv_runtime,hv_relaxed,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce \ -m 2048 \ -device pci-bridge,id=pci.2,chassis_nr=2,bus=pci.0,addr=0x1f \ -device pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e \ -device piix3-usb-uhci,id=uhci,bus=pci.0,addr=0x1.0x2 \ -device usb-tablet,id=tablet,bus=uhci.0,port=1 \ -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 \ -iscsi initiator-name=iqn.1993-08.org.debian:01:1ba48d46fb8 \ -drive if=none,id=drive-ide0,media=cdrom,aio=threads \ -device ide-cd,bus=ide.0,unit=0,drive=drive-ide0,id=ide0,bootindex=200 \ -device virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5 \ -drive file=/mnt/pve/data1/images/101/vm-101-disk-1.qcow2,if=none,id=drive-scsi0,cache=writeback,discard=on,format=qcow2,aio=threads,detect-zeroes=unmap \ -device scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100 \ -netdev type=tap,id=net0,ifname=tap101i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on \ -device virtio-net-pci,mac=F2:2B:20:37:E6:D7,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300 \ -rtc driftfix=slew,base=localtime \ -global kvm-pit.lost_tick_policy=discard To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1618431/+subscriptions
