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

[Daniel Henrique Barboza <danielhb413@gmail.com>]

On 9/4/20 7:02 AM, Greg Kurz wrote:
> 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


That all makes sense to me. I'll introduce a VCPU_ASSOC_SIZE in spapr_numa.h
and use it when operating the associativity for vcpus, both in this patch
and also in patch 3.


Thanks,


DHB


> 
>> -    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));
> 
>>   }
>>   
>>   
>