Re: [Qemu-devel] [PATCH 22/22] add cpu-add qmp command and implement CPU hot-add for target-i386

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 5 Apr 2013 14:24:35 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Fri, Apr 05, 2013 at 02:10:54PM -0300, Eduardo Habkost wrote:
> > On Fri, Apr 05, 2013 at 04:37:16PM +0200, Igor Mammedov wrote:
> > [...]
> > > diff --git a/qapi-schema.json b/qapi-schema.json
> > > index db542f6..a760ed5 100644
> > > --- a/qapi-schema.json
> > > +++ b/qapi-schema.json
> > > @@ -1387,6 +1387,17 @@
> > >  { 'command': 'cpu', 'data': {'index': 'int'} }
> > >  
> > >  ##
> > > +# @cpu-add
> > > +#
> > > +# Adds CPU with specified id
> > > +#
> > > +# @id: cpu id of CPU to be created
> > 
> > Can we have the semantics/constraints of "id" documented here? Is it an
> > arbitrary ID chosen by the caller? Does it have to be the APIC ID? Does
> > it have to be the index of the CPU in the CPU list? How the IDs of
> > existing CPUs set using "-smp" are allocated?
> > 
> > I am looking at the code right now to understand how this implementation
> > works, but the documentation could contain or point to documentation on
> > how the "id" parameter is used and interpreted.
> 
> So, the answer to my own question seems to be on patch 21/22. Let me
> check if I understand this correctly:
> 
>  @id: cpu id of the CPU to be created. It must be one of the the
>       available IDs listed at the "/machine/icc-bridge/cpu[0..N]" links.
> 
> Is the above correct?
yes.

> 
> Now, my question is: suppose a caller starts QEMU as:
> 
>  $ qemu -smp 18,cores=3,threads=3,maxcpus=36 \
>         -numa node,cpus=0-8   -numa node,cpus=9-17 \
>         -numa node,cpus=18-26 -numa node,cpus=27-35
> 
> and the caller wants to hot-add all VCPUs in the last CPU socket (that
> means: all the VCPUs in the last NUMA node, that means: CPU indexes
> 27-35). What should the caller do to find out which of the
> /machine/icc-bridge/cpu[0..N] links/IDs really correspond to those
> VCPUs?
If one wants plug in a specific CPU, It won't work with -numa yet.

to make it work we need to specify sockets on -numa cmd. line and then
construct synthetic QOM containers tree that could looklike:

/machine/numa_nodes/[0..N]/sockets/[0..M]/cpus/[0..X]

then command line could look like:
$ qemu -smp 18,cores=3,threads=3,maxcpus=36 \
       -numa node,sockets=0-1 -numa node,sockets=2-3
> 
> 
> > 
> > > +#
> > > +# Returns: Nothing on success
> > > +##
> > > +{ 'command': 'cpu-add', 'data': {'id': 'int'} }
> > > +
> > > +##
> > -- 
> > Eduardo
> > 
> 
> -- 
> Eduardo
> 


-- 
Regards,
  Igor