Re: [PATCH v3 3/3] cpus-common: implement dirty limit on vCPU

[Markus Armbruster <armbru@redhat.com>]

huangy81@chinatelecom.cn writes:

> From: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
>
> implement dirtyrate calculation periodically basing on
> dirty-ring and throttle vCPU until it reachs the quota
> dirtyrate given by user.
>
> introduce qmp commands set-dirty-limit/cancel-dirty-limit to
> set/cancel dirty limit on vCPU.

Please start sentences with a capital letter.

>
> Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>

[...]

> diff --git a/qapi/misc.json b/qapi/misc.json
> index 358548a..98e6001 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -527,3 +527,42 @@
>   'data': { '*option': 'str' },
>   'returns': ['CommandLineOptionInfo'],
>   'allow-preconfig': true }
> +
> +##
> +# @set-dirty-limit:
> +#
> +# This command could be used to cap the vCPU memory load, which is also
> +# refered as dirtyrate. One should use "calc-dirty-rate" with "dirty-ring"
> +# and to calculate vCPU dirtyrate and query it with "query-dirty-rate".
> +# Once getting the vCPU current dirtyrate, "set-dirty-limit" can be used
> +# to set the upper limit of dirtyrate for the interested vCPU.

"dirtyrate" is not a word.  Let's spell it "dirty page rate", for
consistency with the documentation in migration.json.

Regarding "One should use ...": sounds like you have to run
calc-dirty-rate with argument @mode set to @dirty-ring before this
command.  Correct?  What happens when you don't?  set-dirty-limit fails?

Do you also have to run query-dirty-rate before this command?

Speaking of migration.json: should these commands be defined there, next
to calc-dirty-rate and query-dirty-rate?

> +#
> +# @idx: vCPU index to set dirtylimit.
> +#
> +# @dirtyrate: upper limit of drityrate the specified vCPU could reach (MB/s)

Typo "drityrate".

Suggest "upper limit for the specified vCPU's dirty page rate (MB/s)".

> +#
> +# Since: 6.3
> +#
> +# Example:
> +#   {"execute": "set-dirty-limit"}
> +#    "arguments": { "idx": 0,
> +#                   "dirtyrate": 200 } }
> +#
> +##
> +{ 'command': 'set-dirty-limit',
> +  'data': { 'idx': 'int', 'dirtyrate': 'uint64' } }
> +
> +##
> +# @cancel-dirty-limit:
> +#
> +# @idx: vCPU index to canceled the dirtylimit
> +#
> +# Since: 6.3
> +#
> +# Example:
> +#   {"execute": "cancel-dirty-limit"}
> +#    "arguments": { "idx": 0 } }
> +#
> +##
> +{ 'command': 'cancel-dirty-limit',
> +  'data': { 'idx': 'int' } }
> diff --git a/softmmu/vl.c b/softmmu/vl.c
> index 1159a64..170ee23 100644
> --- a/softmmu/vl.c
> +++ b/softmmu/vl.c
> @@ -3776,5 +3776,6 @@ void qemu_init(int argc, char **argv, char **envp)
>      qemu_init_displays();
>      accel_setup_post(current_machine);
>      os_setup_post();
> +    dirtylimit_setup(current_machine->smp.max_cpus);
>      resume_mux_open();
>  }