Bug 890636

Description of problem:
Boot a guest and run some memory stress test inside it. And then do live migration with xbzrle enabled. Set migration speed to 100M and xbzrle cache size to 4G. During migration, at the beginning migration speed is about 100M (or a little smaller than 100M) when the xbzrle pages have NOT been transferred. But then the migration speed is very slow (about 1M/s) after xbzrle pages are transferred.

Version-Release number of selected component (if applicable):
Install tree: RHEL-7.0-20121217.0
kernel-3.6.0-0.29.el7.x86_64
qemu-kvm-1.2.0-21.el7.x86_64

Guest: RHEL6.4

How reproducible:
Always

Steps to Reproduce:
1. Boot a guest on source host:

 /usr/libexec/qemu-kvm -cpu SandyBridge -enable-kvm -m 2048 -smp 2,sockets=2,cores=1,threads=1 -enable-kvm -name t2-rhel6.4-32 -uuid 61b6c504-5a8b-4fe1-8347-6c929b750dde -k en-us -rtc base=localtime,clock=host,driftfix=slew -no-kvm-pit-reinjection -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device usb-tablet,id=input0 -drive file=/root/rhel6.4-64-virtio.qcow2,if=none,id=disk0,format=qcow2,werror=stop,rerror=stop,aio=native -device ide-drive,bus=ide.0,unit=1,drive=disk0,id=disk0  -drive file=/root/boot.iso,if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw -device ide-drive,drive=drive-ide0-1-0,bus=ide.1,unit=0,id=cdrom -netdev tap,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=44:37:E6:5E:91:85,bus=pci.0,addr=0x5 -monitor stdio -qmp tcp:0:6666,server,nowait -chardev socket,path=/tmp/isa-serial,server,nowait,id=isa1 -device isa-serial,chardev=isa1,id=isa-serial1 -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x8 -chardev socket,id=charchannel0,path=/tmp/serial-socket,server,nowait -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.rhevm.vdsm -chardev socket,path=/tmp/foo,server,nowait,id=foo -device virtconsole,chardev=foo,id=console0  -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x9 -vnc :10 -k en-us -boot c -chardev socket,path=/tmp/qga.sock,server,nowait,id=qga0 -device virtserialport,bus=virtio-serial0.0,chardev=qga0,name=org.qemu.guest_agent.0  -global  PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0

2. Boot guest with listening mode on dst host.

3. Running stress inside guest. #stress -m 2

4. (qemu) migrate_set_capability xbzrle on (on both src and dst)
(qemu) info migrate_capabilities 
capabilities: xbzrle: on 

(qemu) migrate_set_cache_size 4G
(qemu)
(qemu) migrate_set_speed 100m

5. Start migration
(qemu) migrate -d tcp:t2:5800

6. (qemu)info migration (implement this command every 1 sec)

  
Actual results:
After xbzrle starts to be transferred, the migration speed is about 1M/s

Expected results:
Migration speed should be always around 100M/s

Additional info:

(qemu) info migrate
capabilities: xbzrle: on 
Migration status: active
total time: 1811764 milliseconds
transferred ram: 2977037 kbytes
remaining ram: 144208 kbytes
total ram: 2113920 kbytes
duplicate: 6873272 pages
normal: 485325 pages
normal bytes: 1941300 kbytes
cache size: 4294967296 bytes
xbzrle transferred: 1029025 kbytes
xbzrle pages: 8039876 pages
xbzrle cache miss: 485213
xbzrle overflow : 112

1 sec later, check it again:

(qemu) info migrate
capabilities: xbzrle: on 
Migration status: active
total time: 1812644 milliseconds
transferred ram: 2977410 kbytes
remaining ram: 233488 kbytes
total ram: 2113920 kbytes
duplicate: 6876453 pages
normal: 485325 pages
normal bytes: 1941300 kbytes
cache size: 4294967296 bytes
xbzrle transferred: 1029395 kbytes
xbzrle pages: 8042926 pages
xbzrle cache miss: 485213
xbzrle overflow : 112
(qemu)