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


From: Ben Accelance
Subject: Re: [Qemu-devel] Qemu savevm and CPU soft lockup
Date: Wed, 23 Sep 2009 20:52:40 +0200




Le 23 sept. 2009 à 20:19, Jamie Lokier <address@hidden> a écrit :

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


Thanks for this, at least it clarifies things. Now sorry for the pain , but how do you migrate to a file and then how do you restore from the file ?
Thanks
Cheers

Benjamin Cleyet-Marrel



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