Re: [libvirt] [Qemu-devel] [PATCH v4] XBZRLE delta for live migration of large memory apps
From: Anthony Liguori [mailto:anthony@codemonkey.ws]
Sent: Wednesday, August 10, 2011 10:28 PM
To: Avi Kivity
Cc: Blue Swirl; Stefan Hajnoczi; Shribman, Aidan; qemu-devel
Developers; libvir-list(a)redhat.com
Subject: Re: [Qemu-devel] [PATCH v4] XBZRLE delta for live migration of
large memory apps
a) A query-migration-caps command that returns a dict with two lists
of
strings. Something like:
{ 'execute': 'query-migration-caps' }
{ 'return' : { 'capabilities': [ 'xbzrle' ], 'current':
[] } }
b) A set-migration-caps command that takes a list of strings. It
simply
takes the intersection of the capabilities set with the argument and
sets the current set to the result. Something like:
{ 'execute': 'set-migration-caps', 'arguments': { 'set':
[ 'xbzrle' ]
}}
{ 'return' : {} }
We may want to further sub-divide capabilities into categories:
{ 'execute': 'query-migration-caps' }
{ 'return' :
{ 'encoding' : { 'current', 'asn.1', 'proto2',
'thrift', etc. } },
{ 'delta' : { 'xbzrle', "xdelta", ...} },
{ 'compression' : { 'snappy', 'lzo' } } }
This would help libvirt/management to select features automatically or manually (via UI)
without having to 'understand' the any given capability meaning.
Yes. But that negotiation needs to become part of the
"protocol" for
migration. In the absence of that negotiation, we need to use the wire
protocol we use today. We cannot have ad-hoc feature negotiation for
every change we make to the wire protocol.
Agreed. Therefore caps plus xbzrle could be added before ASN.1/v1.0 without breaking
anything as long as when 'set-migration-caps' is not issued Qemu uses the current
protocol.
Aidan