Re: [PATCH v11 3/4] softmmu/dirtylimit: implement virtual CPU throttle

[Markus Armbruster]

huangy81@chinatelecom.cn writes:

> From: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
>
> Setup a negative feedback system when vCPU thread
> handling KVM_EXIT_DIRTY_RING_FULL exit by introducing
> throttle_us_per_full field in struct CPUState. Sleep
> throttle_us_per_full microseconds to throttle vCPU
> if dirtylimit is enabled.
>
> Start a thread to track current dirty page rates and
> tune the throttle_us_per_full dynamically untill current
> dirty page rate reach the quota.
>
> Introduce the util function in the header for dirtylimit
> implementation.
>
> Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>

[...]

> diff --git a/qapi/migration.json b/qapi/migration.json
> index bbfd48c..ac5fa56 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -1850,6 +1850,25 @@
>  { 'command': 'query-dirty-rate', 'returns': 'DirtyRateInfo' }
>  
>  ##
> +# @DirtyLimitInfo:
> +#
> +# Dirty page rate limit information of virtual CPU.
> +#
> +# @cpu-index: index of virtual CPU.
> +#
> +# @limit-rate: upper limit of dirty page rate for virtual CPU.

Lacks a unit.  Is it bytes per second?  pages per second?

If I understand your code correctly, zero means unlimited.  This is
undocumented.  Please document it.  Something like "0 means unlimited"
should do.

> +#
> +# @current-rate: current dirty page rate for virtual CPU.
> +#
> +# Since: 7.0
> +#
> +##
> +{ 'struct': 'DirtyLimitInfo',
> +  'data': { 'cpu-index': 'int',
> +            'limit-rate': 'int64',
> +            'current-rate': 'int64' } }

The next patch uses 'uint64' for set-vcpu-dirty-limit argument
dirty-rate.  Why signed here?

> +
> +##
>  # @snapshot-save:
>  #
>  # Save a VM snapshot

[...]