Re: [PATCH] spapr_numa.c: fixes in spapr_numa_FORM2_write_rtas_tables()

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

On 9/22/21 08:17, Philippe Mathieu-Daudé wrote:
> On 9/21/21 21:43, Daniel Henrique Barboza wrote:
>> This patch has a handful of modifications for the recent added
>> FORM2 support:
>>
>> - there is no particular reason for both 'lookup_index_table' and
>> 'distance_table' to be allocated in the heap, since their sizes are
>> known right at the start of the function. Use static allocation in
>> them to spare a couple of g_new0() calls;
>>
>> - to not allocate more than the necessary size in 'distance_table'. At
>> this moment the array is oversized due to allocating uint32_t for all
>> elements, when most of them fits in an uint8_t;
>>
>> - create a NUMA_LOCAL_DISTANCE macro to avoid hardcoding the local
>> distance value.
>>
>> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
>> ---
>>   hw/ppc/spapr_numa.c | 35 +++++++++++++++++++----------------
>>   1 file changed, 19 insertions(+), 16 deletions(-)
>>
>> diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c
>> index 58d5dc7084..039a0439c6 100644
>> --- a/hw/ppc/spapr_numa.c
>> +++ b/hw/ppc/spapr_numa.c
>> @@ -19,6 +19,9 @@
>>   /* Moved from hw/ppc/spapr_pci_nvlink2.c */
>>   #define SPAPR_GPU_NUMA_ID           (cpu_to_be32(1))
>> +/* Macro to avoid hardcoding the local distance value */
>> +#define NUMA_LOCAL_DISTANCE         10
>> +
>>   /*
>>    * Retrieves max_dist_ref_points of the current NUMA affinity.
>>    */
>> @@ -500,17 +503,21 @@ static void spapr_numa_FORM2_write_rtas_tables(SpaprMachineState *spapr,
>>       MachineState *ms = MACHINE(spapr);
>>       NodeInfo *numa_info = ms->numa_state->nodes;
>>       int nb_numa_nodes = ms->numa_state->num_nodes;
>> +    /* Lookup index table has an extra uint32_t with its length */
>> +    uint32_t lookup_index_table[nb_numa_nodes + 1];
>>       int distance_table_entries = nb_numa_nodes * nb_numa_nodes;
>> -    g_autofree uint32_t *lookup_index_table = NULL;
>> -    g_autofree uint32_t *distance_table = NULL;
>> -    int src, dst, i, distance_table_size;
>> -    uint8_t *node_distances;
> 
> This should have be of ptrdiff_t type.
> 
>> +    /*
>> +     * Distance table is an uint8_t array with a leading uint32_t
>> +     * containing its length.
>> +     */
>> +    uint8_t distance_table[distance_table_entries + 4];
> 
> The previous code seems better by using the heap, now we have
> to worry about stack overflow...


Fair point.

Since no one asked for this change in previous reviews I guess it's fine to keep
using the heap.


Daniel


> 
>> +    uint32_t *distance_table_length;
> 
> Please drop, ...
> 
>> +    int src, dst, i;
>>       /*
>>        * ibm,numa-lookup-index-table: array with length and a
>>        * list of NUMA ids present in the guest.
>>        */
>> -    lookup_index_table = g_new0(uint32_t, nb_numa_nodes + 1);
>>       lookup_index_table[0] = cpu_to_be32(nb_numa_nodes);
>>       for (i = 0; i < nb_numa_nodes; i++) {
>> @@ -518,8 +525,7 @@ static void spapr_numa_FORM2_write_rtas_tables(SpaprMachineState *spapr,
>>       }
>>       _FDT(fdt_setprop(fdt, rtas, "ibm,numa-lookup-index-table",
>> -                     lookup_index_table,
>> -                     (nb_numa_nodes + 1) * sizeof(uint32_t)));
>> +                     lookup_index_table, sizeof(lookup_index_table)));
>>       /*
>>        * ibm,numa-distance-table: contains all node distances. First
>> @@ -531,11 +537,10 @@ static void spapr_numa_FORM2_write_rtas_tables(SpaprMachineState *spapr,
>>        * array because NUMA ids can be sparse (node 0 is the first,
>>        * node 8 is the second ...).
>>        */
>> -    distance_table = g_new0(uint32_t, distance_table_entries + 1);
>> -    distance_table[0] = cpu_to_be32(distance_table_entries);
>> +    distance_table_length = (uint32_t *)distance_table;
>> +    distance_table_length[0] = cpu_to_be32(distance_table_entries);
> 
> ... and use instead:
> 
>         stl_be_p(distance_table, distance_table_entries);
> 
>> -    node_distances = (uint8_t *)&distance_table[1];
>> -    i = 0;
>> +    i = 4;
>>       for (src = 0; src < nb_numa_nodes; src++) {
>>           for (dst = 0; dst < nb_numa_nodes; dst++) {
>> @@ -546,18 +551,16 @@ static void spapr_numa_FORM2_write_rtas_tables(SpaprMachineState *spapr,
>>                * adding the numa_info to retrieve distance info from.
>>                */
>>               if (src == dst) {
>> -                node_distances[i++] = 10;
>> +                distance_table[i++] = NUMA_LOCAL_DISTANCE;
>>                   continue;
>>               }
>> -            node_distances[i++] = numa_info[src].distance[dst];
>> +            distance_table[i++] = numa_info[src].distance[dst];
>>           }
>>       }
>> -    distance_table_size = distance_table_entries * sizeof(uint8_t) +
>> -                          sizeof(uint32_t);
>>       _FDT(fdt_setprop(fdt, rtas, "ibm,numa-distance-table",
>> -                     distance_table, distance_table_size));
>> +                     distance_table, sizeof(distance_table)));
>>   }
>>   /*
>>
>