Re: [PATCH v2 06/29] migration: Add auto-pause capability

[Markus Armbruster]

Fabiano Rosas <farosas@suse.de> writes:

> Add a capability that allows the management layer to delegate to QEMU
> the decision of whether to pause a VM and perform a non-live
> migration. Depending on the type of migration being performed, this
> could bring performance benefits.
>
> Note that the capability is enabled by default but at this moment no
> migration scheme is making use of it.

This sounds as if the capability has no effect unless the "migration
scheme" (whatever that may be) opts into using it.  Am I confused?

> Signed-off-by: Fabiano Rosas <farosas@suse.de>

[...]

> diff --git a/qapi/migration.json b/qapi/migration.json
> index db3df12d6c..74f12adc0e 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -523,6 +523,10 @@
>  #     and can result in more stable read performance.  Requires KVM
>  #     with accelerator property "dirty-ring-size" set.  (Since 8.1)
>  #
> +# @auto-pause: If enabled, allows QEMU to decide whether to pause the
> +#     VM before migration for an optimal migration performance.
> +#     Enabled by default. (since 8.1)

If this needs an opt-in to take effect, it should be documented.

> +#
>  # Features:
>  #
>  # @unstable: Members @x-colo and @x-ignore-shared are experimental.
> @@ -539,7 +543,7 @@
>             { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
>             'validate-uuid', 'background-snapshot',
>             'zero-copy-send', 'postcopy-preempt', 'switchover-ack',
> -           'dirty-limit'] }
> +           'dirty-limit', 'auto-pause'] }
>  
>  ##
>  # @MigrationCapabilityStatus: