Re: [Qemu-devel] [RFC PATCH v2 3/5] spapr: Set stable_cpu_id for threads of CPU cores

[Greg Kurz]

On Fri, 8 Jul 2016 15:25:33 +1000
David Gibson <address@hidden> wrote:

> On Thu, Jul 07, 2016 at 06:11:31PM +0200, Greg Kurz wrote:
> > On Thu,  7 Jul 2016 20:20:23 +0530
> > Bharata B Rao <address@hidden> wrote:
> >   
> > > Conditonally set stable_cpu_id for CPU threads that are created as part
> > > of spapr CPU cores. The use of stable_cpu_id is enabled for pseries-2.7
> > > onwards.
> > >   
> > 
> > The last sentence is a bit confusing since the enablement actually happens
> > in patch 5/5.
> >   
> > > Signed-off-by: Bharata B Rao <address@hidden>
> > > ---
> > >  hw/ppc/spapr_cpu_core.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > > index b104778..0ec3513 100644
> > > --- a/hw/ppc/spapr_cpu_core.c
> > > +++ b/hw/ppc/spapr_cpu_core.c
> > > @@ -293,8 +293,15 @@ static void spapr_cpu_core_realize(DeviceState *dev, 
> > > Error **errp)
> > >      for (i = 0; i < cc->nr_threads; i++) {
> > >          char id[32];
> > >          obj = sc->threads + i * size;
> > > +        CPUState *cs;
> > >  
> > >          object_initialize(obj, size, typename);
> > > +        cs = CPU(obj);
> > > +
> > > +        /* Use core_id (which is actually cpu_dt_id) as stable CPU id */ 
> > >  
> > 
> > It isn't what I had in mind. More something like below:
> > 
> > In ppc_spapr_init():
> > 
> >     for (i = 0; i < spapr_max_cores; i++) {
> >         spapr->cores[i]->stable_id = i * smp_threads;
> >     }
> > 
> > 
> > In spapr_cpu_core_realize():
> > 
> >     for (j = 0; j < cc->nr_threads; j++) {
> >         stable_cpu_id = cc->stable_id + j;
> >     }
> > 
> > So we need to introduce cc->stable_id.  
> 
> No, we don't.  Cores have had a stable ID since they were introduced.
> 

I agree core_dt_id is stable but it is a DT concept.

static void ppc_spapr_init(MachineState *machine)
{
[...]
        for (i = 0; i < spapr_max_cores; i++) {
            int core_dt_id = i * smt;
[...]
                object_property_set_int(core, core_dt_id, CPU_CORE_PROP_CORE_ID,
                                        &error_fatal);

This patch produces stable_cpu_id in the [0...smt * smp_cores) range. I find it
awkward it depends on the host setup.

I'm suggesting we introduce cc->stable_id to be able to compute a simple
stable_cpu_id in the range [0...max_cpus), like x86 and ARM.

> Instead we should be setting the thread stable ids based on the core
> stable id.
> 
> > I think stable_cpu_id is the prerequisite to compute both cpu_dt_id and 
> > instance_id.
> > 
> > Makes sense ?
> >   
> > > +        if (cs->has_stable_cpu_id) {
> > > +            cs->stable_cpu_id = cc->core_id + i;
> > > +        }
> > >          snprintf(id, sizeof(id), "thread[%d]", i);
> > >          object_property_add_child(OBJECT(sc), id, obj, &local_err);
> > >          if (local_err) {  
> >   
>

pgpuPmvr4S1wT.pgp
Description: OpenPGP digital signature