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

[Hyman Huang]

在 2021/12/16 14:22, Peter Xu 写道:
> On Wed, Dec 15, 2021 at 02:41:32PM +0100, Markus Armbruster wrote:
> > 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.
>
> Fair enough. :)  That looks good to me too.
>
> Yong, please hold-off a bit on reposting (if there's a plan) - I'll read the
> other parts soon..
Ok, i'm not going to repost the next version untill the consensus is 
achieved.

So the final format of qmp we conclude are:

case 1: setup vcpu 0 dirty page limit 100MB/s
set-vcpu-dirty-limit cpu-index=0 dirty-rate=100

case 2: setup all vcpu dirty page limit 100MB/s
set-vcpu-dirty-limit dirty-rate=100

case 3: cancel vcpu 0 dirty page limit
cancel-vcpu-dirty-limit cpu-index=0

case 4: cancel all vcpu dirty page limit
cancel-vcpu-dirty-limit

case 5: query limit infomatioin of all vcpu enabled
query-vcpu-dirty-limit

And the corresponding hmp format keep the same style:

Is there any advice? :)

> Thanks,

--
Best regard

Hyman Huang(黄勇)