[Qemu-devel] BUG: RTC issue when Windows guest is idle

[Matthew Anderson]

If this isn't the correct list just let me know,

I've run into a bug whereby a Windows guest (tested on Server 2008R2 and 2012) 
no longer receives RTC ticks when it has been idle for a random amount of time. 
HPET is disabled and the guest is running Hyper-V relaxed timers (same 
situation without hv_relaxed). The guest clock stands still and the qemu 
process uses very little CPU (<0.5%, normally it's >5% when the guest is idle) 
. Eventually the guest stops responding to network requests but if you open the 
guest console via VNC and move the mouse around it comes back to life and QEMU 
replays the lost RTC ticks and the guest recovers. I've also been able to make 
it recover by querying the clock over the network via the net time command, you 
can see the clock stand still for 30 seconds then it replays the ticks and 
catches up.

I've tried to reproduce the issue but it seems fairly illusive, the only way 
I've been able to reproduce it is by letting the VM's idle and waiting. 
Sometimes it's hours and sometimes minutes. Can anyone suggest a way to narrow 
the issue down?

Qemu command line is-
/usr/bin/kvm -name SQL01 -S -M pc-0.14 -cpu qemu64,hv_relaxed -enable-kvm -m 
2048 -smp 2,sockets=2,cores=1,threads=1 -uuid 
5f54333b-c250-aa72-c979-39d156814b85 -no-user-config -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/iHost-SQL01.monitor,server,nowait
 -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime -no-hpet 
-no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive 
file=/mnt/gluster1-norep/iHost/SQL01.qed,if=none,id=drive-virtio-disk0,format=qed,cache=writeback
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0
 -drive 
file=/mnt/gluster1-norep/iHost/SQL01-Data.qed,if=none,id=drive-virtio-disk2,format=qed,cache=writeback
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x6,drive=drive-virtio-disk2,id=virtio-disk2
 -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw -device 
ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0,bootindex=1 -netdev 
tap,fd=29,id=hostnet0,vhost=on,vhostfd=39 -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:2c:8d:23,bus=pci.0,addr=0x3 
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 
-device usb-tablet,id=input0 -vnc 127.0.0.1:22 -vga cirrus -device 
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4

Environment is -
Mainline 3.7.5 and 3.8.0
Qemu 1.2.2, 1.3.1 and 1.4.0
Scientific Linux 6.3
KSM enabled, transparent hugepages disabled.
Dual Xeon 5650
192GB

Thanks all