Re: [Qemu-devel] [PATCH 07/16] migration: Create x-multifd-group parameter

[Daniel P. Berrange]

On Mon, Mar 13, 2017 at 01:44:25PM +0100, Juan Quintela wrote:
> Indicates how many pages we are going to send in each bach to a multifd
> thread.


> diff --git a/qapi-schema.json b/qapi-schema.json
> index b7cb26d..33a6267 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -988,6 +988,9 @@
>  # @x-multifd-threads: Number of threads used to migrate data in parallel
>  #                     The default value is 2 (since 2.9)
>  #
> +# @x-multifd-group: Number of pages sent together to a thread
> +#                     The default value is 16 (since 2.9)
> +#
>  # Since: 2.4
>  ##
>  { 'enum': 'MigrationParameter',
> @@ -995,7 +998,7 @@
>             'cpu-throttle-initial', 'cpu-throttle-increment',
>             'tls-creds', 'tls-hostname', 'max-bandwidth',
>             'downtime-limit', 'x-checkpoint-delay',
> -           'x-multifd-threads'] }
> +           'x-multifd-threads', 'x-multifd-group'] }
>  
>  ##
>  # @migrate-set-parameters:
> @@ -1062,6 +1065,9 @@
>  # @x-multifd-threads: Number of threads used to migrate data in parallel
>  #                     The default value is 2 (since 2.9)
>  #
> +# @x-multifd-group: Number of pages sent together in a bunch
> +#                     The default value is 16 (since 2.9)
> +#

How is this parameter supposed to be used ? Or to put it another way,
what are the benefits / effects of changing it from its default
value and can an application usefully decide what value to set ? I'm
loathe to see us expose another "black magic" parameter where you can't
easily determine what values to set, without predicting future guest
workloads


Regards,
Daniel
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