Re: [Qemu-devel] [PATCH] ppc/pnv: fix cores per chip for multiple cpus

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

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On Wed, Sep 06, 2017 at 01:57:48PM +0530, Nikunj A Dadhania wrote:
> When the user does not provide the cpu topology, e.g. "-smp 4", machine fails to
> initialize 4 cpus. Compute the chip per cores depending on the number of chips
> and smt threads.
> 
> Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>

I don't understand why simply treating smp_cores as cores per chip is wrong.

> ---
>  hw/ppc/pnv.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
> index 9724719..3fbaafb 100644
> --- a/hw/ppc/pnv.c
> +++ b/hw/ppc/pnv.c
> @@ -642,7 +642,7 @@ static void ppc_powernv_init(MachineState *machine)
>      MemoryRegion *ram;
>      char *fw_filename;
>      long fw_size;
> -    int i;
> +    int i, cores_per_chip;
>      char *chip_typename;
>      PCIBus *pbus;
>      bool has_gfx = false;
> @@ -710,6 +710,22 @@ static void ppc_powernv_init(MachineState *machine)
>      }
>  
>      pnv->chips = g_new0(PnvChip *, pnv->num_chips);
> +
> +    /* If user has specified number of cores, use it. Otherwise, compute it. */
> +    if (smp_cores != 1) {
> +        cores_per_chip = smp_cores;
> +    } else {
> +        cores_per_chip = smp_cpus / (smp_threads * pnv->num_chips);
> +    }
> +
> +    if (smp_cpus != (smp_threads * pnv->num_chips * cores_per_chip)) {
> +        error_report("cpu topology not balanced: "
> +                     "chips (%u) * cores (%u) * threads (%u) != "
> +                     "number of cpus (%u)",
> +                     pnv->num_chips, cores_per_chip, smp_threads, smp_cpus);
> +        exit(1);
> +    }
> +
>      for (i = 0; i < pnv->num_chips; i++) {
>          char chip_name[32];
>          Object *chip = object_new(chip_typename);
> @@ -728,7 +744,7 @@ static void ppc_powernv_init(MachineState *machine)
>          object_property_add_child(OBJECT(pnv), chip_name, chip, &error_fatal);
>          object_property_set_int(chip, PNV_CHIP_HWID(i), "chip-id",
>                                  &error_fatal);
> -        object_property_set_int(chip, smp_cores, "nr-cores", &error_fatal);
> +        object_property_set_int(chip, cores_per_chip, "nr-cores", &error_fatal);
>          object_property_set_int(chip, 1, "num-phbs", &error_fatal);
>          object_property_set_bool(chip, true, "realized", &error_fatal);
>      }

-- 
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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