Re: [PATCH 7/7] spapr: Set VSMT to smp_threads by default

[Greg Kurz <groug@kaod.org>]

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On Mon, 14 Oct 2019 17:12:47 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Thu, Oct 03, 2019 at 02:02:00PM +0200, Greg Kurz wrote:
> > Support for setting VSMT is available in KVM since linux-4.13. Most distros
> > that support KVM on POWER already have it. It thus seem reasonable enough
> > to have the default machine to set VSMT to smp_threads.
> > 
> > This brings contiguous VCPU ids and thus brings their upper bound down to
> > the machine's max_cpus. This is especially useful for XIVE KVM devices,
> > which may thus allocate only one VP descriptor per VCPU.
> > 

Just to clarify that without the other patches in this series, XIVE
KVM devices still allocate a fixed block of 2048 VPs, no matter what.
ie, the last sentence in the changelog may be slightly misleading.

> > Signed-off-by: Greg Kurz <groug@kaod.org>
> 
> Applied to ppc-for-4.2, thanks.
> 
> > ---
> >  hw/ppc/spapr.c         |    7 ++++++-
> >  include/hw/ppc/spapr.h |    1 +
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 8f59f08c102e..473ce1d04775 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -2503,6 +2503,7 @@ static CPUArchId *spapr_find_cpu_slot(MachineState *ms, uint32_t id, int *idx)
> >  static void spapr_set_vsmt_mode(SpaprMachineState *spapr, Error **errp)
> >  {
> >      MachineState *ms = MACHINE(spapr);
> > +    SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(spapr);
> >      Error *local_err = NULL;
> >      bool vsmt_user = !!spapr->vsmt;
> >      int kvm_smt = kvmppc_smt_threads();
> > @@ -2529,7 +2530,7 @@ static void spapr_set_vsmt_mode(SpaprMachineState *spapr, Error **errp)
> >              goto out;
> >          }
> >          /* In this case, spapr->vsmt has been set by the command line */
> > -    } else {
> > +    } else if (!smc->smp_threads_vsmt) {
> >          /*
> >           * Default VSMT value is tricky, because we need it to be as
> >           * consistent as possible (for migration), but this requires
> > @@ -2538,6 +2539,8 @@ static void spapr_set_vsmt_mode(SpaprMachineState *spapr, Error **errp)
> >           * overwhelmingly common case in production systems.
> >           */
> >          spapr->vsmt = MAX(8, smp_threads);
> > +    } else {
> > +        spapr->vsmt = smp_threads;
> >      }
> >  
> >      /* KVM: If necessary, set the SMT mode: */
> > @@ -4452,6 +4455,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
> >      smc->irq = &spapr_irq_dual;
> >      smc->dr_phb_enabled = true;
> >      smc->linux_pci_probe = true;
> > +    smc->smp_threads_vsmt = true;
> >  }
> >  
> >  static const TypeInfo spapr_machine_info = {
> > @@ -4519,6 +4523,7 @@ static void spapr_machine_4_1_class_options(MachineClass *mc)
> >  
> >      spapr_machine_4_2_class_options(mc);
> >      smc->linux_pci_probe = false;
> > +    smc->smp_threads_vsmt = false;
> >      compat_props_add(mc->compat_props, hw_compat_4_1, hw_compat_4_1_len);
> >      compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
> >  }
> > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > index cbd1a4c9f390..2009eb64f9cb 100644
> > --- a/include/hw/ppc/spapr.h
> > +++ b/include/hw/ppc/spapr.h
> > @@ -122,6 +122,7 @@ struct SpaprMachineClass {
> >      bool broken_host_serial_model; /* present real host info to the guest */
> >      bool pre_4_1_migration; /* don't migrate hpt-max-page-size */
> >      bool linux_pci_probe;
> > +    bool smp_threads_vsmt; /* set VSMT to smp_threads by default */
> >  
> >      void (*phb_placement)(SpaprMachineState *spapr, uint32_t index,
> >                            uint64_t *buid, hwaddr *pio, 
> > 
> 


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