Re: [Qemu-devel] [PATCH v4] XBZRLE delta for live migration of large memory apps

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/08/2011 09:47 AM, Avi Kivity 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
>> it isn't effective.
>>
>
> IOW, this should be part of the standard migration protocol, not some
> side option that is enabled if the user remembers. It should not be
> mutually exclusive with future migration extensions, including compression.

Are you thinking of a static decision or a dynamic decision?

I think feature negotiation would address static decision making.  For 
dynamic decision making, you could look to something like the VNC 
protocol and how it encodes pixel data.  The flow looks something like:

1) All clients/servers must support raw encoding

2) Client presents list of support encodings

3) Server takes intersection of client supported encodings and server 
supported encodings.

4) Server can choose to encode updates using any encoding supported by 
client and server.

Regards,

Anthony Liguori