Re: [PATCH 2/2] ppc/pnv: Use the CPU topology to compute the default number of chips

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Dec 20, 2019 at 05:51:48PM +0100, Greg Kurz wrote:
> Multi TCG mandates the CPU topology to be dimensioned to the actual
> number of CPUs, depending on the number of chips the user asked for.
> That is, '-machine num-chips=N' should always have a '-smp' companion
> with a topology that meats the resulting number of CPUs, typically
> '-smp sockets=N'.
> 
> Simplify the command line for these setups by computing the default
> number of chips based on the CPU topology, ie. no need to explicitely
> set "num-chips" anymore. This must be done at machine init because
> smp_parse() is called after instance init.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>

Is there actually any reason to retain num-chips at all?  Or could we
just set the number of chips equal to the number of sockets, which
seems to make sense to me.

> ---
>  hw/ppc/pnv.c |   23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index f8cf2b6d760f..9b777b7084a0 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -768,6 +768,19 @@ static void pnv_init(MachineState *machine)
>          exit(1);
>      }
>  
> +    if (!pnv->num_chips) {
> +        uint32_t num_chips =
> +            machine->smp.max_cpus / (machine->smp.cores * machine->smp.threads);
> +        Error *local_err = NULL;
> +
> +        object_property_set_uint(OBJECT(pnv), num_chips, "num-chips",
> +                                 &local_err);
> +        if (local_err) {
> +            error_report_err(local_err);
> +            exit(1);
> +        }
> +    }
> +
>      pnv->chips = g_new0(PnvChip *, pnv->num_chips);
>      for (i = 0; i < pnv->num_chips; i++) {
>          char chip_name[32];
> @@ -1722,6 +1735,9 @@ static void pnv_set_num_chips(Object *obj, Visitor *v, const char *name,
>       */
>      if (!is_power_of_2(num_chips) || num_chips > 4) {
>          error_setg(errp, "invalid number of chips: '%d'", num_chips);
> +        error_append_hint(errp,
> +                          "Set 'num-chips' implicitely with '-smp sockets=N'. "
> +                          "Valid values are : 1, 2 or 4.\n");
>          return;
>      }
>  
> @@ -1735,12 +1751,6 @@ static void pnv_set_num_chips(Object *obj, Visitor *v, const char *name,
>      pnv->num_chips = num_chips;
>  }
>  
> -static void pnv_machine_instance_init(Object *obj)
> -{
> -    PnvMachineState *pnv = PNV_MACHINE(obj);
> -    pnv->num_chips = 1;
> -}
> -
>  static void pnv_machine_class_props_init(ObjectClass *oc)
>  {
>      object_class_property_add(oc, "num-chips", "uint32",
> @@ -1874,7 +1884,6 @@ static const TypeInfo types[] = {
>          .parent        = TYPE_MACHINE,
>          .abstract       = true,
>          .instance_size = sizeof(PnvMachineState),
> -        .instance_init = pnv_machine_instance_init,
>          .class_init    = pnv_machine_class_init,
>          .class_size    = sizeof(PnvMachineClass),
>          .interfaces = (InterfaceInfo[]) {
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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