Re: [RFC PATCH 5/5] spapr: Allow up to 8 threads SMT configuration

[Cédric Le Goater]

On 6/2/23 08:59, Nicholas Piggin wrote:
> On Thu Jun 1, 2023 at 5:20 PM AEST, Cédric Le Goater wrote:
> > On 5/31/23 03:23, Nicholas Piggin wrote:
> > > TCG now supports multi-threaded configuration at least enough for
> > > pseries to be functional enough to boot Linux.
> > >
> > > This requires PIR and TIR be set, because that's how sibling thread
> > > matching is done.
> > >
> > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > > ---
> > >    hw/ppc/spapr.c          | 4 ++--
> > >    hw/ppc/spapr_cpu_core.c | 7 +++++--
> > >    2 files changed, 7 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index dcb7f1c70a..11074cefea 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -2524,8 +2524,8 @@ static void spapr_set_vsmt_mode(SpaprMachineState *spapr, 
> > > Error **errp)
> > >        int ret;
> > >        unsigned int smp_threads = ms->smp.threads;
> > >    
> > > -    if (!kvm_enabled() && (smp_threads > 1)) {
> > > -        error_setg(errp, "TCG cannot support more than 1 thread/core "
> > > +    if (!kvm_enabled() && (smp_threads > 8)) {
> > > +        error_setg(errp, "TCG cannot support more than 8 threads/core "
> > >                       "on a pseries machine");
> >
> > I think we should add test on the CPU also.
>
> On the CPU type, POWER7 can have 1/2/4, POWER8 can have 1/2/4/8?
> POWER9 could also switch PVR between big and small core depending
> on whether you select SMT8 I suppose.

What I meant is to limit the support to the CPUs which will be most likely
used : POWER8-10. I don't think we care much about the others P7, P5+, 970.

Thanks,

C.