Re: [Qemu-devel] [PATCH 7/9] spapr: Limit threads per core according to current compatibility mode

[Alexander Graf <agraf@suse.de>]

On 15.05.14 13:28, Alexey Kardashevskiy wrote:
> This puts a limit to the number of threads per core based on the current
> compatibility mode. Although PowerISA specs do not specify the maximum
> threads per core number, the linux guest still expects that
> PowerISA2.05-compatible CPU supports only 2 threads per core as this
> is what POWER6 (2.05 compliant CPU) implements, same is true for
> POWER7 (2.06, 4 threads) and POWER8 (2.07, 8 threads).
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>   hw/ppc/spapr.c | 31 ++++++++++++++++++++++++++++---
>   1 file changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index cf53a7a..a2c9106 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -34,6 +34,7 @@
>   #include "sysemu/kvm.h"
>   #include "kvm_ppc.h"
>   #include "mmu-hash64.h"
> +#include "cpu-models.h"
>   
>   #include "hw/boards.h"
>   #include "hw/ppc/ppc.h"
> @@ -203,6 +204,29 @@ static XICSState *xics_system_init(int nr_servers, int nr_irqs)
>       return icp;
>   }
>   
> +static int spapr_get_compat_smp_threads(PowerPCCPU *cpu)
> +{
> +    int ret = -1;
> +
> +    switch (cpu->cpu_version) {
> +    case CPU_POWERPC_LOGICAL_2_05:
> +        ret = 2;
> +        break;
> +    case CPU_POWERPC_LOGICAL_2_06:
> +        ret = 4;
> +        break;
> +    case CPU_POWERPC_LOGICAL_2_07:
> +        ret = 8;
> +        break;
> +    default:
> +        ret = smp_threads;
> +        break;
> +    }
> +    ret = MIN(ret, smp_threads);

Just call this in the function where you set the compat property and 
error out if threads > supported_threads. We always default to 1 thread 
anyway, so the only thing that could get us a broken configuration is 
the user.


Alex