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Re: [Qemu-devel] [RFC 0/2] Disable hotplug during migration

From: Juan Quintela
Subject: Re: [Qemu-devel] [RFC 0/2] Disable hotplug during migration
Date: Wed, 29 Mar 2017 12:41:19 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Juan Quintela (address@hidden) wrote:
>> Hi
>> This series disable hotplug/unplug during migration.  Thank to Markus
>> for explaining where I had to put the checks.  Why?  Because during
>> migration we will fail if there are changes.  For instance, in
>> postcopy, if we add a memory region, we would failing.  Same for other
>> devices if they are not setup exactly the same on destination.
>> Iidea would be to disable it, andthen enable for the thing that we know that 
>> work.
>> This series are on top of my previous RAMState v2 serie.
>> Commets, please?
> So I think this is probably a good idea, but we should ask Li Zhijian who 
> added
> migration_bitmap_extend if the reason for adding it was because they
> needed the hot add to work.
> cc'd.

I guess that the problem for them is that the bitmap size was wrong
after memory resizing.  But I don't know if this has ever worked.

> IMHO we really need a 'configuration change mutex' that you can take
> to stop any changes in the VM hardware, and that would probably reduce
> a lot of the places that hold the BQL for just stopping changes.

That was the previous patch.  With that one, you can't add/remove
hardware during migration.

Later, Juan.

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