[libvirt-users] virsh hangs when backup jobs run on the kvm host

[Eric Blake]

On 3/2/19 9:23 PM, Zhan Adlun wrote:
> Hi,
>     Has anyone met the same problem that virsh hangs when there are some backup jobs running on the kvm host? I use dirty bitmap supported by qemu to do backups every 6 minitues. About a few hours later, I ran 'virsh list', It hung.  Then I stopped the backup jobs ，nothing was getting better. I had checked the libvirt logs ，but found nothing useful .

How are you using dirty bitmaps?  As my new virDomainBackupBegin() API
has not landed yet, I suspect you are using virQemuMonitorCommand()
(virsh qemu-monitor-command) backdoors, which is explicitly unsupported
(that is, if it breaks, you get to debug it - it exists for development
work, and while 'query-*' QMP commands should be safe, commands that
alter qemu state such as kicking off a backup job may break libvirt
expectations), and which is WHY I'm trying to get incremental backup API
officially supported.

A precise sequence of commands that you issued in order to reproduce the
virsh hang may be useful in debugging this.

>     Maybe the high I/O caused the problem? or there are connection number limits when using virsh, because I use virsh to check the backup jobs are still running every 10 seconds?
>     My os version is ' Ubuntu 12.04 LTS   Release: 12.04   Codename: precise,Linux version 4.1.0-generic (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #1 SMP Wed Nov 9 02:04:23 CST 2016'. KVM version is 'QEMU emulator version 2.7.1(Debian 1:2.7+dfsg-3)'. Hoping for you reply. Thanks!

Hmm, my incremental backup API will require qemu 4.0; there have been a
number of fixes in the qemu bitmap tracking that have landed since qemu
2.7.1. It could also be that you've hit an actual qemu bug where the QMP
monitor has gone unresponsive.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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