Re: [PATCH v4 2/3] spapr_numa: create a vcpu associativity helper

[Greg Kurz <groug@kaod.org>]

On Thu,  3 Sep 2020 22:04:38 -0300
Daniel Henrique Barboza <danielhb413@gmail.com> wrote:

> The work to be done in h_home_node_associativity() intersects
> with what is already done in spapr_numa_fixup_cpu_dt(). This
> patch creates a new helper, spapr_numa_get_vcpu_assoc(), to
> be used for both spapr_numa_fixup_cpu_dt() and
> h_home_node_associativity().
> 
> While we're at it, use memcpy() instead of loop assignment
> to created the returned array.
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---

Hi Daniel,

A few comments below.

>  hw/ppc/spapr_numa.c | 30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c
> index 368c1a494d..980a6488bf 100644
> --- a/hw/ppc/spapr_numa.c
> +++ b/hw/ppc/spapr_numa.c
> @@ -71,13 +71,15 @@ void spapr_numa_write_associativity_dt(SpaprMachineState *spapr, void *fdt,
>                        sizeof(spapr->numa_assoc_array[nodeid]))));
>  }
>  
> -int spapr_numa_fixup_cpu_dt(SpaprMachineState *spapr, void *fdt,
> -                            int offset, PowerPCCPU *cpu)
> +static uint32_t *spapr_numa_get_vcpu_assoc(SpaprMachineState *spapr,
> +                                          PowerPCCPU *cpu,
> +                                          uint *vcpu_assoc_size)
>  {
> -    uint vcpu_assoc_size = NUMA_ASSOC_SIZE + 1;
> -    uint32_t vcpu_assoc[vcpu_assoc_size];
> +    uint32_t *vcpu_assoc = NULL;

You don't need to initialize this pointer since it is assigned a value
unconditionally just below.

>      int index = spapr_get_vcpu_id(cpu);
> -    int i;
> +
> +    *vcpu_assoc_size = (NUMA_ASSOC_SIZE + 1) * sizeof(uint32_t);

It's a bit weird to return something that is definitely a compile
time constant by reference... What about introducing a macro ?

#define VCPU_NUMA_ASSOC_SIZE (NUMA_ASSOC_SIZE + 1)

> +    vcpu_assoc = g_malloc(*vcpu_assoc_size);
>  

    vcpu_assoc = g_new(uint32_t, VCPU_NUMA_ASSOC_SIZE);

>      /*
>       * VCPUs have an extra 'cpu_id' value in ibm,associativity
> @@ -86,16 +88,24 @@ int spapr_numa_fixup_cpu_dt(SpaprMachineState *spapr, void *fdt,
>       * cpu_id last.
>       */
>      vcpu_assoc[0] = cpu_to_be32(MAX_DISTANCE_REF_POINTS + 1);
> +    memcpy(vcpu_assoc + 1, spapr->numa_assoc_array[cpu->node_id],
> +           MAX_DISTANCE_REF_POINTS);
> +    vcpu_assoc[MAX_DISTANCE_REF_POINTS + 1] = cpu_to_be32(index);
>  

    memcpy(vcpu_assoc + 1, spapr->numa_assoc_array[cpu->node_id],
           (VPCU_ASSOC_SIZE - 2) * sizeof(uint32_t));
    vcpu_assoc[VCPU_ASSOC_SIZE - 1] = cpu_to_be32(index);

I personally find more clear than using MAX_DISTANCE_REF_POINTS in an array
that was just allocated with NUMA_ASSOC_SIZE... one has to check spapr.h
to see that NUMA_ASSOC_SIZE == MAX_DISTANCE_REF_POINTS + 1

> -    for (i = 1; i <= MAX_DISTANCE_REF_POINTS; i++) {
> -        vcpu_assoc[i] = spapr->numa_assoc_array[cpu->node_id][i];
> -    }
> +    return vcpu_assoc;
> +}
> +
> +int spapr_numa_fixup_cpu_dt(SpaprMachineState *spapr, void *fdt,
> +                            int offset, PowerPCCPU *cpu)
> +{
> +    g_autofree uint32_t *vcpu_assoc = NULL;
> +    uint vcpu_assoc_size;
>  
> -    vcpu_assoc[vcpu_assoc_size - 1] = cpu_to_be32(index);
> +    vcpu_assoc = spapr_numa_get_vcpu_assoc(spapr, cpu, &vcpu_assoc_size);
>  
>      /* Advertise NUMA via ibm,associativity */
>      return fdt_setprop(fdt, offset, "ibm,associativity",
> -                       vcpu_assoc, sizeof(vcpu_assoc));
> +                       vcpu_assoc, vcpu_assoc_size);

    return fdt_setprop(fdt, offset, "ibm,associativity",
                       vcpu_assoc, VCPU_NUMA_ASSOC_SIZE * sizeof(uint32_t));

>  }
>  
>