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

[Greg Kurz <groug@kaod.org>]

On Tue, 21 Sep 2021 16:43:47 -0300
Daniel Henrique Barboza <danielhb413@gmail.com> 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.
> 

Not needed. A notion of minimal distance, which is obviously
synonymous to local, already exists in the "sysemu/numa.h"
header :

#define NUMA_DISTANCE_MIN         10

> 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;
> +    /*
> +     * Distance table is an uint8_t array with a leading uint32_t
> +     * containing its length.
> +     */
> +    uint8_t distance_table[distance_table_entries + 4];
> +    uint32_t *distance_table_length;
> +    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);
>  
> -    node_distances = (uint8_t *)&distance_table[1];
> -    i = 0;
> +    i = 4;
>  

A comment reminding why we're doing that wouldn't hurt, e.g.

/* Skip the array size (uint32_t) */

With these fixed, especially using NUMA_DISTANCE_MIN, you
can add:

Reviewed-by: Greg Kurz <groug@kaod.org>

>      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)));
>  }
>  
>  /*