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Date: Mon, 8 Aug 2011 15:56:03 +0100
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From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH v4] XBZRLE delta for live migration of
 large memory apps
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To: Avi Kivity <avi@redhat.com>
Cc: Blue Swirl <blauwirbel@gmail.com>, "Shribman,
	Aidan" <aidan.shribman@sap.com>, qemu-devel Developers <qemu-devel@nongnu.org>

On Mon, Aug 8, 2011 at 3:47 PM, Avi Kivity <avi@redhat.com> wrote:
> On 08/08/2011 05:46 PM, Avi Kivity wrote:
>>
>> Please provide documentation in docs/ of the compression format.
>>
>> IMO it should be disabled by default (with an option to disable it, via,
>> sat, migrate-set-options, so we can migrate to older hosts).
>>
>> The protocol should allow XBZRLE to turn itself off if it detects that i=
t
>> isn't effective.
>>
>
> IOW, this should be part of the standard migration protocol, not some sid=
e
> option that is enabled if the user remembers. =A0It should not be mutuall=
y
> exclusive with future migration extensions, including compression.

This is an attractive option.  With some polish maybe XBZRLE could be
integrated as a default option that does not degrade performance.
Adding features that require user configuration isn't worthwhile
because they won't be used or they'll be misused - let's not make QEMU
more complicated if it can be avoided.

If there is no way to make XBZRLE automatic then I think it should
live outside QEMU because it will be a niche feature that relatively
few will use but adds complexity to migration.

Stefan