Re: [PATCH RFC v1 3/3] qapi/iothread: introduce poll-weight parameter for aio-poll

[Markus Armbruster <armbru@redhat.com>]

Jaehoon Kim <jhkim@linux.ibm.com> writes:

> Introduce a new poll-weight parameter for aio-poll. This parameter
> controls how much the most recent event interval affects the next
> polling duration. When set to 0, a default value of 2 is used, meaning
> the current interval contributes roughly 25% to the calculation. Larger
> values decrease the weight of the current interval, enabling more
> gradual adjustments to polling duration.
>
> Signed-off-by: Jaehoon Kim <jhkim@linux.ibm.com>

[...]

> diff --git a/qapi/misc.json b/qapi/misc.json
> index 28c641fe2f..b21cc48a03 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -85,6 +85,11 @@
>  # @poll-shrink: how many ns will be removed from polling time, 0 means
>  #     that it's not configured (since 2.9)
>  #
> +# @poll-weight: the weight factor for adaptive polling.
> +#     Determines how much the current event interval contributes to
> +#     the next polling time calculation.  0 means that the default
> +#     value is used.  (since 10.1)

When the default value is used, the actual value being used remains
hidden.  Why?

> +#
>  # @aio-max-batch: maximum number of requests in a batch for the AIO
>  #     engine, 0 means that the engine will use its default (since 6.1)
>  #
> @@ -96,6 +101,7 @@
>             'poll-max-ns': 'int',
>             'poll-grow': 'int',
>             'poll-shrink': 'int',
> +           'poll-weight': 'int',
>             'aio-max-batch': 'int' } }
>  
>  ##
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 6f5c9de0f0..d90823478d 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -606,6 +606,11 @@
>  #     algorithm detects it is spending too long polling without
>  #     encountering events.  0 selects a default behaviour (default: 0)
>  #
> +# @poll-weight: the weight factor for adaptive polling.
> +#     Determines how much the current event interval contributes to
> +#     the next polling time calculation.  0 selects a default
> +#     behaviour (default: 0) since 10.1.

This leaves the actual default behavior unspecified.  Is this a good
idea?

> +#
>  # The @aio-max-batch option is available since 6.1.
>  #
>  # Since: 2.0
> @@ -614,7 +619,8 @@
>    'base': 'EventLoopBaseProperties',
>    'data': { '*poll-max-ns': 'int',
>              '*poll-grow': 'int',
> -            '*poll-shrink': 'int' } }
> +            '*poll-shrink': 'int',
> +            '*poll-weight': 'int' } }
>  
>  ##
>  # @MainLoopProperties:

[...]