Re: [PATCH v10 3/3] cpus-common: implement dirty page limit on virtual CPU

[Markus Armbruster <armbru@redhat.com>]

Peter Xu <peterx@redhat.com> writes:

> On Wed, Dec 15, 2021 at 03:56:55PM +0800, Hyman Huang wrote:
>> > > +{ 'command': 'vcpu-dirty-limit',
>> > > +  'data': { 'enable': 'bool',
>> > > +            '*cpu-index': 'uint64',
>> > > +            '*dirty-rate': 'uint64'} }
>> > 
>> > Drop @enable, please.
>> > 
>> > If @dirty-rate is present, set the limit to its value.
>> > 
>> > If it's absent, cancel the limit.
>> > 
>> Ok. Indeed, this is the simplest style. :)
>> 
>> So the final qmp format should be like:
>> 
>> case 1: setup vcpu 0 dirty page limit 100MB/s
>> vcpu-dirty-limit  cpu-index=0   dirty-rate=100MB/s
>> 
>> case 2: cancle vcpu 0 dirty page limit
>> vcpu-dirty-limit  cpu-index=0
>
> I actually agree with what you said... for human beings no one will read it as
> "disable vcpu throttling", instead people could consider it enables vcpu
> throttle with a default dirty rate from a gut feeling.
>
> I think what Markus suggested is the simplest solution for computers, but it
> can confuse human beings.  So it turns out to be a general question to QMP
> scheme design: should we always assume QMP client to be a piece of software, or
> should we still consider the feeling of human beings operating on QMP
> interfaces using qmp-shell.
>
> IMHO we should still consider the latter, if we don't lose much, anyway.  But I
> don't have a strong opinion.

If you want a more explicit interface, then I'd recommend to go right
back to v7:

    {"execute": "set-vcpu-dirty-limit",
     "arguments": {"cpu-index": 0, "dirtyrate": 200}}

    {"execute": "cancel-vcpu-dirty-limit",
     "arguments": {"cpu-index": 0}}

Bonus: it already has my Acked-by.