Re: [Qemu-devel] [PATCH 04/17] ppc: Add number of threads per core to the processor definition

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2016-03-15 at 20:45 +1100, David Gibson wrote:
> On Mon, Mar 14, 2016 at 05:56:27PM +0100, Cédric Le Goater wrote:
> > 
> > From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > 
> > Also use it to clamp the max SMT mode and ensure that the cpu_dt_id
> > are offset by that value in order to preserve consistency with the
> > HW implementations.

> I think this can change change CPU ids, and therefore break migration
> on some existing setups.  So it will need some rework to apply at
> all, and will certainly want to wait until after 2.6

Our migration is so bloody damn fragile ... grrr.

We will need it for powernv though, there are many things especially in
OPAL that rely on the consistent numbering.

In fact, it will have to go further and number the cores based on their
equivalent HW numbers at some point for SCOMs to work, which means a
slightly discontiguous numbering scheme (no core 0 for example). At
least if we want to model some of the EX XSCOMs.

Cheers,
Ben.

> > 
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> >  target-ppc/cpu-qom.h        |  1 +
> >  target-ppc/translate_init.c | 11 ++++++++++-
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/target-ppc/cpu-qom.h b/target-ppc/cpu-qom.h
> > index 7d5e2b36a997..735981309c5b 100644
> > --- a/target-ppc/cpu-qom.h
> > +++ b/target-ppc/cpu-qom.h
> > @@ -68,6 +68,7 @@ typedef struct PowerPCCPUClass {
> >      uint32_t flags;
> >      int bfd_mach;
> >      uint32_t l1_dcache_size, l1_icache_size;
> > +    uint32_t threads_per_core;
> >  #if defined(TARGET_PPC64)
> >      const struct ppc_segment_page_sizes *sps;
> >  #endif
> > diff --git a/target-ppc/translate_init.c b/target-
> > ppc/translate_init.c
> > index 43c6e524a6bc..46dabe58783a 100644
> > --- a/target-ppc/translate_init.c
> > +++ b/target-ppc/translate_init.c
> > @@ -8231,6 +8231,7 @@ POWERPC_FAMILY(POWER5P)(ObjectClass *oc, void
> > *data)
> >                   POWERPC_FLAG_BUS_CLK;
> >      pcc->l1_dcache_size = 0x8000;
> >      pcc->l1_icache_size = 0x10000;
> > +    pcc->threads_per_core = 2;
> >  }
> >  
> >  static void powerpc_get_compat(Object *obj, Visitor *v, const char
> > *name,
> > @@ -8408,6 +8409,7 @@ POWERPC_FAMILY(POWER7)(ObjectClass *oc, void
> > *data)
> >      pcc->l1_dcache_size = 0x8000;
> >      pcc->l1_icache_size = 0x8000;
> >      pcc->interrupts_big_endian =
> > ppc_cpu_interrupts_big_endian_lpcr;
> > +    pcc->threads_per_core = 4;
> >  }
> >  
> >  static void init_proc_POWER8(CPUPPCState *env)
> > @@ -8492,6 +8494,7 @@ POWERPC_FAMILY(POWER8)(ObjectClass *oc, void
> > *data)
> >      pcc->l1_dcache_size = 0x8000;
> >      pcc->l1_icache_size = 0x8000;
> >      pcc->interrupts_big_endian =
> > ppc_cpu_interrupts_big_endian_lpcr;
> > +    pcc->threads_per_core = 8;
> >  }
> >  #endif /* defined (TARGET_PPC64) */
> >  
> > @@ -9195,6 +9198,12 @@ static void ppc_cpu_realizefn(DeviceState
> > *dev, Error **errp)
> >  #endif
> >  
> >  #if !defined(CONFIG_USER_ONLY)
> > +    if (pcc->threads_per_core == 0) {
> > +        pcc->threads_per_core = 1;
> > +    }
> > +    if (max_smt > pcc->threads_per_core) {
> > +        max_smt = pcc->threads_per_core;
> > +    }
> >      if (smp_threads > max_smt) {
> >          error_setg(errp, "Cannot support more than %d threads on
> > PPC with %s",
> >                     max_smt, kvm_enabled() ? "KVM" : "TCG");
> > @@ -9215,7 +9224,7 @@ static void ppc_cpu_realizefn(DeviceState
> > *dev, Error **errp)
> >      }
> >  
> >  #if !defined(CONFIG_USER_ONLY)
> > -    cpu->cpu_dt_id = (cs->cpu_index / smp_threads) * max_smt
> > +    cpu->cpu_dt_id = (cs->cpu_index / smp_threads) * pcc-
> > >threads_per_core
> >          + (cs->cpu_index % smp_threads);
> >  #endif
> >