Re: [Qemu-devel] Qemu savevm and CPU soft lockup

[Jamie Lokier <jamie@shareable.org>]

Benjamin Cleyet-Marrel wrote:
> 
>    Hi,
>    After further investigation, I figured out that when issuing a savevm
>    command
>    the entire qemu process gets stuck on IO wait.
>    I can't issue any other commands on the monitor the process is shown
>    as D and the guest is in softlockup state.
>    Looking at the way migrate (and the -d for detach I presume) is
>    working I suppose the same behaviour would be expected from the savevm
>    function.
>    A savevm -d so that the qemu process would not be freezed while saving
>    the data.
>    Sorry if I am just talking non sense but my snapshot on iscsi storage
>    takes about 1 minutes.
>    which means that my guest are down for a minute or so which is not
>    ideal.

This is normal savevm behaviour, and it is exactly the reason why
migrate-to-file is useful.  I would not be surprised if savevm is
changed to use migrate-to-file internally at some point, but it does
not look like happening soon.

You might avoid the guest softlockup state by stopping the guest
("stop" command) before savevm, and "cont" afterwards?

Or the guest might get just as confused, as the clock still advances.

-- Jamie