On Thu, Jul 28, 2022 at 08:32:39PM +0530, Het Gala wrote:
>
> On 26/07/22 4:43 pm, Daniel P. Berrangé wrote:
> > On Thu, Jul 21, 2022 at 07:56:15PM +0000, Het Gala wrote:
> > > i) Modified the format of the qemu monitor command : 'migrate' by adding
> > > a list,
> > > each element in the list consisting of multifd connection parameters:
> > > source
> > > uri, destination uri and of the number of multifd channels between
> > > each pair.
> > >
> > > ii) Information of all multifd connection parameters' list and length of
> > > the
> > > list is stored in 'OutgoingMigrateParams' struct.
> > >
> > > Suggested-by: Manish Mishra <manish.mis...@nutanix.com>
> > > Signed-off-by: Het Gala <het.g...@nutanix.com>
> > > ---
> > > migration/migration.c | 52 +++++++++++++++++++++++++++++--------
> > > migration/socket.c | 60 ++++++++++++++++++++++++++++++++++++++++---
> > > migration/socket.h | 19 +++++++++++++-
> > > monitor/hmp-cmds.c | 1 +
> > > qapi/migration.json | 47 +++++++++++++++++++++++++++++----
> > > 5 files changed, 160 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/qapi/migration.json b/qapi/migration.json
> > > index 81185d4311..456247af8f 100644
> > > --- a/qapi/migration.json
> > > +++ b/qapi/migration.json
> > > @@ -1449,12 +1449,37 @@
> > > ##
> > > { 'command': 'migrate-continue', 'data': {'state': 'MigrationStatus'} }
> > > +##
> > > +# @MigrateUriParameter:
> > > +#
> > > +# Information regarding which source interface is connected to which
> > > +# destination interface and number of multifd channels over each
> > > interface.
> > > +#
> > > +# @source-uri: uri of the source VM. Default port number is 0.
> > > +#
> > > +# @destination-uri: uri of the destination VM
> > > +#
> > > +# @multifd-channels: number of parallel multifd channels used to migrate
> > > data
> > > +# for specific source-uri and destination-uri.
> > > Default value
> > > +# in this case is 2 (Since 7.1)
> > > +#
> > > +##
> > > +{ 'struct' : 'MigrateUriParameter',
> > > + 'data' : { 'source-uri' : 'str',
> > > + 'destination-uri' : 'str',
> > > + '*multifd-channels' : 'uint8'} }
> > > +
> > > ##
> > > # @migrate:
> > > #
> > > # Migrates the current running guest to another Virtual Machine.
> > > #
> > > # @uri: the Uniform Resource Identifier of the destination VM
> > > +# for migration thread
> > > +#
> > > +# @multi-fd-uri-list: list of pair of source and destination VM Uniform
> > > +# Resource Identifiers with number of
> > > multifd-channels
> > > +# for each pair
> > > #
> > > # @blk: do block migration (full disk copy)
> > > #
> > > @@ -1474,20 +1499,32 @@
> > > # 1. The 'query-migrate' command should be used to check migration's
> > > progress
> > > # and final result (this information is provided by the 'status'
> > > member)
> > > #
> > > -# 2. All boolean arguments default to false
> > > +# 2. The uri argument should have the Uniform Resource Identifier of
> > > default
> > > +# destination VM. This connection will be bound to default network
> > > #
> > > -# 3. The user Monitor's "detach" argument is invalid in QMP and should
> > > not
> > > +# 3. All boolean arguments default to false
> > > +#
> > > +# 4. The user Monitor's "detach" argument is invalid in QMP and should
> > > not
> > > # be used
> > > #
> > > # Example:
> > > #
> > > -# -> { "execute": "migrate", "arguments": { "uri": "tcp:0:4446" } }
> > > +# -> { "execute": "migrate",
> > > +# "arguments": {
> > > +# "uri": "tcp:0:4446",
> > > +# "multi-fd-uri-list": [ { "source-uri": "tcp::6900",
> > > +# "destination-uri": "tcp:0:4480",
> > > +# "multifd-channels": 4},
> > > +# { "source-uri": "tcp:10.0.0.0: ",
> > > +# "destination-uri":
> > > "tcp:11.0.0.0:7789",
> > > +# "multifd-channels": 5} ] } }
> > > # <- { "return": {} }
> > > #
> > > ##
> > > { 'command': 'migrate',
> > > - 'data': {'uri': 'str', '*blk': 'bool', '*inc': 'bool',
> > > - '*detach': 'bool', '*resume': 'bool' } }
> > > + 'data': {'uri': 'str', '*multi-fd-uri-list': ['MigrateUriParameter'],
> > > + '*blk': 'bool', '*inc': 'bool', '*detach': 'bool',
> > > + '*resume': 'bool' } }
> > Considering the existing migrate API from a QAPI design POV, I
> > think there are several significant flaws with it
> >
> > The use of URIs is the big red flag. It is basically a data encoding
> > scheme within a data encoding scheme. QEMU code should be able to
> > directly work with the results from QAPI, without having todo a
> > second level of parsing.
> >
> > URIs made sense in the context of HMP or the QemuOpts CLI, but do not
> > make sense in QMP. We made a mistake in this respect when we first
> > introduced QMP and implemented 'migrate'.
> >
> > If we going to extend the migrate API I think we should stop using URIs
> > for the new fields, and instead define a QAPI discriminated union for
> > the different data transport backends we offer.
> >
> > { 'enum': 'MigrateTransport',
> > 'data': ['socket', 'exec'] }
> >
> > { 'union': 'MigrateAddress',
> > 'base': { 'transport': 'MigrateTransport'},
> > 'discriminator': 'transport',
> > 'data': {
> > 'socket': 'SocketAddress',
> > 'exec': ['str'],
> > }
> >
> > NB, 'socket' should be able to cover all of 'tcp', 'unix', 'vsock'
> > and 'fd' already. I'm fuzzy on best way to represent RDMA.
> >
> >
> > IIUC, the desire of migration maintainers is that we can ultimately
> > have multifd as the preferred, or even only, mechanism. Aside from
> > the main outbound migration control channel, and the multifd
> > data channels, IIUC we have a potential desire to have more channels
> > for post-copy async requests.
> >
> > This all suggests to me a more general representation along the
> > lines of:
> >
> > { 'enum': 'MigrateChannelType',
> > 'data': ['control', 'data', 'async'] }
> >
> > { 'struct': 'MigrateChannel',
> > 'data': {
> > 'type': 'MigrateChannelType',
> > 'src-addr': 'MigrateAddress',
> > 'dst-addr': 'MigrateAddress',
> > 'count': 'int',
> > } }
> >
> > { 'comand': 'migrate',
> > 'data': {
> > '*uri': 'str'
> > '*channels': ['MigrateChannel']
> > }
> > }
> >
> > With 'uri' and 'channels' being mutually exclusive here.
> >
> > This whole scheme brings in redundancy wrt to the 'migrate-set-parameters'
> > API wrt multifd - essentally the same data is now being set in two
> > different places. IMHO, we should declare the 'multifd' capability
> > and the 'multifd-chanels' parameter deprecated, since the information
> > they provide is totally redundant, if you're giving an explicit list
> > of channels to 'migrate'.
> > Hi Daniel. Initially while brainstorming this idea for the first time, we
> also came up with the same thought of depricating the migrate API. But how
> will we achieve this now and how is it going to work. Is it like we will be
> making migate V2 APIs initially, integrate it and then depricate the old
> one? would be happy to get some pointers from your end.
I don't think we need to replace 'migrate' with 'migrate2', because our
QAPI deprecation & feature addition policy lets us evolve the existing
commands over time.
We currently have
{ 'comand': 'migrate',
'data': {
'uri': 'str'
}
}
Our ABI policy lets us make 'uri' optional, and as well as adding new
optional fields:
{ 'comand': 'migrate',
'data': {
'*uri': 'str'
'*channels': ['MigrateChannel']
}
}
At some point we can choose to deprecate 'uri' entirely and just ask
people to use a single element 'channels' array. After having 'uri'
deprecated for a while we can delete it and make 'channels' mandatory
{ 'comand': 'migrate',
'data': {
'channels': ['MigrateChannel']
}
}
This gives us the same end point as if we had added
{ 'comand': 'migrate2',
'data': {
'channels': ['MigrateChannel']
}
}
and deprecated &deleted 'migrate' entirely, but without leaving us with
the ugly naming.
FWIW, if I was going to majorly refactor migration QAPI design, I would
also seek to get rid of 'migrate-set-capability' entirely and just
make it a parameter to 'migrate', and likewise for the same for any of
'migrate-set-parameter' that are only used as upfront tunables. We
should only need 'migrate-set-parameter' for runtime tunables that need
setting /after/ migration has already started. I didn't mention this
before though, as I didn't want to impose a big chunk of extra work
on this feature of yours, as it can be done separately at any time.
With regards,
Daniel
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