Re: [PATCH v2 16/24] migration: Add capabilities into MigrationParameters

[Markus Armbruster <armbru@redhat.com>]

Fabiano Rosas <farosas@suse.de> writes:

> Add capabilities to MigrationParameters. This structure will hold all
> migration options. Capabilities will go away in the next patch.
>
> Also add capabilities to MigrationParameter as the enum needs to be
> kept in sync with MigrationParameters. This affects the parsing of
> migration HMP commands so make the necessary additions there too.
>
> From this point on, both QMP and HMP versions of
> migrate-set-parameters and query-migrate-parameters gain the ability
> to work with capabilities.
>
> With MigrationParameters now having members for each capability, the
> migration capabilities commands (query-migrate-capabilities,
> migrate-set-capabilities) will soon be deprecated. Add a set of
> helpers to convert between the old MigrationCapability representation
> and the new representation as members of MigrationParameters.
>
> Signed-off-by: Fabiano Rosas <farosas@suse.de>

[...]

> diff --git a/qapi/migration.json b/qapi/migration.json
> index 40e00fb86e..3d3f5624c5 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -763,7 +763,14 @@
>             'vcpu-dirty-limit',
>             'mode',
>             'zero-page-detection',
> -           'direct-io'] }
> +           'direct-io', 'xbzrle', 'rdma-pin-all', 'auto-converge',
> +           'zero-blocks', 'events', 'postcopy-ram', 'x-colo',
> +           'release-ram', 'return-path', 'pause-before-switchover',
> +           'multifd', 'dirty-bitmaps', 'postcopy-blocktime',
> +           'late-block-activate', 'x-ignore-shared',
> +           'validate-uuid', 'background-snapshot',
> +           'zero-copy-send', 'postcopy-preempt',
> +           'switchover-ack', 'dirty-limit', 'mapped-ram' ] }

This is MigrateParameter.  Different order than in MigrationParameters.
Intentional?

>  
>  ##
>  # @migrate-set-parameters:
> @@ -934,10 +941,108 @@
>  #     only has effect if the @mapped-ram capability is enabled.
>  #     (Since 9.1)
>  #
> +# @xbzrle: Migration supports xbzrle (Xor Based Zero Run Length
> +#     Encoding).  This feature allows us to minimize migration traffic
> +#     for certain work loads, by sending compressed difference of the
> +#     pages
> +#
> +# @rdma-pin-all: Controls whether or not the entire VM memory
> +#     footprint is mlock()'d on demand or all at once.  Refer to
> +#     docs/rdma.txt for usage.  Disabled by default.  (since 2.0)
> +#
> +# @zero-blocks: During storage migration encode blocks of zeroes
> +#     efficiently.  This essentially saves 1MB of zeroes per block on
> +#     the wire.  Enabling requires source and target VM to support
> +#     this feature.  To enable it is sufficient to enable the
> +#     capability on the source VM.  The feature is disabled by
> +#     default.  (since 1.6)
> +#
> +# @events: generate events for each migration state change (since 2.4)
> +#
> +# @auto-converge: If enabled, QEMU will automatically throttle down
> +#     the guest to speed up convergence of RAM migration.  (since 1.6)
> +#
> +# @postcopy-ram: Start executing on the migration target before all of
> +#     RAM has been migrated, pulling the remaining pages along as
> +#     needed.  The capacity must have the same setting on both source
> +#     and target or migration will not even start.  NOTE: If the

Make this

   #     and target or migration will not even start.  **Note:** if the

Crossed with commit 188b31ad425c (qapi: Use proper markup instead of
CAPS for emphasis in doc comments).

> +#     migration fails during postcopy the VM will fail.  (since 2.6)
> +#
> +# @x-colo: If enabled, migration will never end, and the state of the
> +#     VM on the primary side will be migrated continuously to the VM
> +#     on secondary side, this process is called COarse-Grain LOck
> +#     Stepping (COLO) for Non-stop Service.  (since 2.8)
> +#
> +# @release-ram: if enabled, qemu will free the migrated ram pages on

And this

   # @release-ram: if enabled, QEMU will free the migrated ram pages on

Crossed with commit 6263225492ba (qapi: Correct spelling of QEMU in doc
comments).

> +#     the source during postcopy-ram migration.  (since 2.9)
> +#
> +# @return-path: If enabled, migration will use the return path even
> +#     for precopy.  (since 2.10)
> +#
> +# @pause-before-switchover: Pause outgoing migration before
> +#     serialising device state and before disabling block IO (since
> +#     2.11)

   #     serialising device state and before disabling block IO
   #     (since 2.11)

Crossed with commit c1a6aa1d443e (qapi: Avoid breaking lines within
(since X.Y))

> +#
> +# @multifd: Use more than one fd for migration (since 4.0)
> +#
> +# @dirty-bitmaps: If enabled, QEMU will migrate named dirty bitmaps.
> +#     (since 2.12)
> +#
> +# @postcopy-blocktime: Calculate downtime for postcopy live migration
> +#     (since 3.0)
> +#
> +# @late-block-activate: If enabled, the destination will not activate
> +#     block devices (and thus take locks) immediately at the end of
> +#     migration.  (since 3.0)
> +#
> +# @x-ignore-shared: If enabled, QEMU will not migrate shared memory
> +#     that is accessible on the destination machine.  (since 4.0)
> +#
> +# @validate-uuid: Send the UUID of the source to allow the destination
> +#     to ensure it is the same.  (since 4.2)
> +#
> +# @background-snapshot: If enabled, the migration stream will be a
> +#     snapshot of the VM exactly at the point when the migration
> +#     procedure starts.  The VM RAM is saved with running VM.
> +#     (since 6.0)
> +#
> +# @zero-copy-send: Controls behavior on sending memory pages on
> +#     migration.  When true, enables a zero-copy mechanism for sending
> +#     memory pages, if host supports it.  Requires that QEMU be
> +#     permitted to use locked memory for guest RAM pages.  (since 7.1)
> +#
> +# @postcopy-preempt: If enabled, the migration process will allow
> +#     postcopy requests to preempt precopy stream, so postcopy
> +#     requests will be handled faster.  This is a performance feature
> +#     and should not affect the correctness of postcopy migration.
> +#     (since 7.1)
> +#
> +# @switchover-ack: If enabled, migration will not stop the source VM
> +#     and complete the migration until an ACK is received from the
> +#     destination that it's OK to do so.  Exactly when this ACK is
> +#     sent depends on the migrated devices that use this feature.  For
> +#     example, a device can use it to make sure some of its data is
> +#     sent and loaded in the destination before doing switchover.
> +#     This can reduce downtime if devices that support this capability
> +#     are present.  'return-path' capability must be enabled to use
> +#     it.  (since 8.1)
> +#
> +# @dirty-limit: If enabled, migration will throttle vCPUs as needed to
> +#     keep their dirty page rate within @vcpu-dirty-limit.  This can
> +#     improve responsiveness of large guests during live migration,
> +#     and can result in more stable read performance.  Requires KVM
> +#     with accelerator property "dirty-ring-size" set.  (Since 8.1)
> +#
> +# @mapped-ram: Migrate using fixed offsets in the migration file for
> +#     each RAM page.  Requires a migration URI that supports seeking,
> +#     such as a file.  (since 9.0)
> +#
>  # Features:
>  #
> -# @unstable: Members @x-checkpoint-delay and
> -#     @x-vcpu-dirty-limit-period are experimental.
> +# @unstable: Members @x-checkpoint-delay, @x-vcpu-dirty-limit-period,
> +#     @x-colo and @x-ignore-shared are experimental.
> +# @deprecated: Member @zero-blocks is deprecated as being part of
> +#     block migration which was already removed.
>  #
>  # Since: 2.4
>  ##
> @@ -972,7 +1077,29 @@
>              '*vcpu-dirty-limit': 'uint64',
>              '*mode': 'MigMode',
>              '*zero-page-detection': 'ZeroPageDetection',
> -            '*direct-io': 'bool' } }
> +            '*direct-io': 'bool',
> +            '*xbzrle': 'bool',
> +            '*rdma-pin-all': 'bool',
> +            '*auto-converge': 'bool',
> +            '*zero-blocks': { 'type': 'bool', 'features': [ 'deprecated' ] },
> +            '*events': 'bool',
> +            '*postcopy-ram': 'bool',
> +            '*x-colo': { 'type': 'bool', 'features': [ 'unstable' ] },
> +            '*release-ram': 'bool',
> +            '*return-path': 'bool',
> +            '*pause-before-switchover': 'bool',
> +            '*multifd': 'bool',
> +            '*dirty-bitmaps': 'bool',
> +            '*postcopy-blocktime': 'bool',
> +            '*late-block-activate': 'bool',
> +            '*x-ignore-shared': { 'type': 'bool', 'features': [ 'unstable' ] },
> +            '*validate-uuid': 'bool',
> +            '*background-snapshot': 'bool',
> +            '*zero-copy-send': 'bool',
> +            '*postcopy-preempt': 'bool',
> +            '*switchover-ack': 'bool',
> +            '*dirty-limit': 'bool',
> +            '*mapped-ram': 'bool' } }
>  
>  ##
>  # @query-migrate-parameters: