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Re: [Qemu-devel] [RFC 08/13] pc: add writeonly 'cpu' property to PCMachi


From: Eduardo Habkost
Subject: Re: [Qemu-devel] [RFC 08/13] pc: add writeonly 'cpu' property to PCMachine
Date: Mon, 23 Jan 2017 13:03:50 -0200
User-agent: Mutt/1.7.1 (2016-10-04)

On Mon, Jan 23, 2017 at 12:20:33PM +0530, Bharata B Rao wrote:
> On Thu, Jan 19, 2017 at 04:04:23PM +0100, Igor Mammedov wrote:
> > On Wed, 18 Jan 2017 16:57:13 -0200
> > Eduardo Habkost <address@hidden> wrote:
> > 
> > > On Wed, Jan 18, 2017 at 06:13:24PM +0100, Igor Mammedov wrote:
> > > > it will allow generic numa code to set cpu to numa node mapping
> > > > in target independent manner in the next patch.
> > > > 
> > > > Signed-off-by: Igor Mammedov <address@hidden>
> > > > ---
> > > >  hw/i386/pc.c | 56 
> > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > >  1 file changed, 56 insertions(+)
> > > > 
> > > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > > index f8ea635..1d33a5e 100644
> > > > --- a/hw/i386/pc.c
> > > > +++ b/hw/i386/pc.c
> > > > @@ -2201,6 +2201,56 @@ static void pc_machine_set_pit(Object *obj, bool 
> > > > value, Error **errp)
> > > >      pcms->pit = value;
> > > >  }
> > > >  
> > > > +static void pc_machine_set_cpu(Object *obj, Visitor *v, const char 
> > > > *name,
> > > > +                               void *opaque, Error **errp)
> > > > +{
> > > > +    uint32_t apic_id;
> > > > +    X86CPUTopoInfo topo;
> > > > +    CPUArchId *cpu_slot;
> > > > +    Error *local_err = NULL;
> > > > +    CpuInstanceProperties *cpu_props = NULL;
> > > > +    PCMachineState *pcms = PC_MACHINE(obj);
> > > > +    MachineClass *mc = MACHINE_GET_CLASS(obj);
> > > > +
> > > > +    visit_type_CpuInstanceProperties(v, name, &cpu_props, &local_err);
> > > > +    if (local_err) {
> > > > +        goto out;
> > > > +    }
> > > > +
> > > > +    if (!cpu_props->has_node_id) {
> > > > +        error_setg(&local_err, "node-id property is not specified");
> > > > +        goto out;
> > > > +    }
> > > > +
> > > > +    /*
> > > > +     * make sure that possible_cpus is initialized
> > > > +     * as property setter might be called before machine init is called
> > > > +     */
> > > > +    mc->possible_cpu_arch_ids(MACHINE(obj));
> > > > +
> > > > +    topo.pkg_id = cpu_props->socket_id;
> > > > +    topo.core_id = cpu_props->core_id;
> > > > +    topo.smt_id = cpu_props->thread_id;
> > > > +    apic_id = apicid_from_topo_ids(smp_cores, smp_threads, &topo);
> > > > +    cpu_slot = pc_find_cpu_slot(pcms, apic_id, NULL);  
> > > 
> > > If we make TYPE_MACHINE provide an API to query CPU slots, e.g.:
> > >   CPUArchId *machine_find_cpu_slot(MachineState *m, CpuInstanceProperties 
> > > *props)
> > so if there is no objections, 
> > I'll move possible_cpus to MachineState
> > and add to MachineClass above callback so target machine
> > would be able to provide arch specific lookup function.
> > it should work for both x86 and ARM.
> 
> The need for possible_cpus in MachineState for sPAPR isn't immediately
> apparent to me. In the context of this new numa "cpu" property, PC target
> seems to use possible_cpus to store and later lookup the numa node id for
> a given CPU. Wondering if that could be achieved w/o needing possible_cpus
> in MachineState ?

We need to save the node ID for not-yet-plugged CPUs somewhere,
and the existing numa_info[].node_cpu field is cpu_index-based so
it needs to be replaced. A MachineState field would allow us to
do that in a generic way.

-- 
Eduardo



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