Re: [Qemu-devel] virtio-serial-pci very expensive during live migration

[Chris Friesen <chris.friesen@windriver.com>]

On 05/08/2014 10:02 AM, Paolo Bonzini wrote:
> Il 08/05/2014 17:57, Chris Friesen ha scritto:
>>>>
>>>> The fact remains that qemu crashes when I apply the patch.  I also
>>>> tried
>>>> patching it as below in virtio_pci_vmstate_change().  That would allow
>>>> the VM to boot, but it would crash when I tried to do a live migration.
>>>
>>> Can you give us your command line and a backtrace?
>>
>> For the backtrace, you mean with a core file?  Or is there a better way?
>
> You can attach gdb to the qemu process, and run "thread apply all bt"
> when QEMU crashes.


For the commandline, it's coming from OpenStack via libvirt, so it's 
fairly complicated:

/usr/bin/kvm -c 0x00000000000000000000000000000001 -n 4 
--proc-type=secondary --file-prefix=vs -- -enable-dpdk -name 
instance-00000007 -S -machine pc-i440fx-1.4,accel=kvm,usb=off -m 512 
-mem-prealloc -mem-path /mnt/huge-2048kB/libvirt/qemu -smp 
2,sockets=2,cores=1,threads=1 -uuid b277d785-9c31-45be-91d3-15b7b1aca974 
-smbios type=1,manufacturer=OpenStack Foundation,product=OpenStack 
Nova,version=2013.2.2,serial=00000000-0000-3848-3342-4e5037313536,uuid=b277d785-9c31-45be-91d3-15b7b1aca974 
-no-user-config -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/instance-00000007.monitor,server,nowait 
-mon chardev=charmonitor,id=monitor,mode=control -rtc 
base=utc,driftfix=slew -no-kvm-pit-reinjection -no-shutdown -device 
piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -device 
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x3 -drive 
file=/etc/nova/instances/b277d785-9c31-45be-91d3-15b7b1aca974/disk,if=none,id=drive-virtio-disk0,format=qcow2,cache=none 
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 
-chardev 
file,id=charserial0,path=/etc/nova/instances/b277d785-9c31-45be-91d3-15b7b1aca974/console.log 
-device isa-serial,chardev=charserial0,id=serial0 -chardev 
pty,id=charserial1 -device isa-serial,chardev=charserial1,id=serial1 
-chardev 
socket,id=charchannel0,path=/var/lib/libvirt/qemu/cgcs.heartbeat.instance-00000007.sock,server,nowait 
-device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=cgcs.heartbeat 
-device usb-tablet,id=input0 -vnc 0.0.0.0:0 -k en-us -vga cirrus -device 
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 -device 
avp,port=4a05cedd-3868-449a-9728-899bbea10863,id=avp4a05cedd-38




As for the backtrace, I can attach gdb to the qemu process, but when I 
hit "c" to continue it gives an error:


Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols 
found)...done.
Loaded symbols for /lib64/libnss_files.so.2

warning: File "/lib64/libthread_db-1.0.so" auto-loading has been 
declined by your `auto-load safe-path' set to 
"$debugdir:$datadir/auto-load".

warning: Unable to find libthread_db matching inferior's thread library, 
thread debugging will not be available.
0x00007f56c6366d23 in select () from /lib64/libc.so.6
(gdb) c
Continuing.
Warning:
Cannot insert breakpoint -1.
Error accessing memory address 0x2f7c50: Input/output error.


Chris