Re: [Qemu-devel] [PATCH 2/2] qmp: document query-cpus performance issue

[Luiz Capitulino]

On Thu, 8 Feb 2018 09:29:28 +0000
Daniel P. Berrangé <address@hidden> wrote:

> On Wed, Feb 07, 2018 at 12:50:14PM -0500, Luiz Capitulino wrote:
> > Signed-off-by: Luiz Capitulino <address@hidden>
> > ---
> >  qapi-schema.json | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index 82d6f12b53..0665a14dba 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -526,6 +526,10 @@
> >  #
> >  # Returns a list of information about each virtual CPU.
> >  #
> > +# WARNING: This command incurs a performance penalty for latency
> > +#          sensitive workloads and hence it's not recommended to
> > +#          to be used in production. Use query-cpus-fast instead  
> 
> I suggest being more explicit about exactly what the problem is, so people
> understand implications if they choose to still use it. ie

I'll add your text.

> 
>   This command causes vCPU threads to exit to userspace, which causes
>   an small interruption guest CPU execution. This will have a negative
>   impact on realtime guests and other latency sensitive guest workloads.
>   It is recommended to use query-cpus-fast instead of this command to
>   avoid the vCPU interruption.
> 
> Regards,
> Daniel