Re: [PATCH 1/2] numa: Set default distance map if needed

[Andrew Jones]

On Wed, Oct 06, 2021 at 06:22:08PM +0800, Gavin Shan wrote:
> The following option is used to specify the distance map. It's
> possible the option isn't provided by user. In this case, the
> distance map isn't populated and exposed to platform. On the
> other hand, the empty NUMA node, where no memory resides, is
> allowed on ARM64 virt platform. For these empty NUMA nodes,
> their corresponding device-tree nodes aren't populated, but
> their NUMA IDs should be included in the "/distance-map"
> device-tree node, so that kernel can probe them properly if
> device-tree is used.
> 
>   -numa,dist,src=<numa_id>,dst=<numa_id>,val=<distance>
> 
> So when user doesn't specify distance map, we need to generate
> the default distance map, where the local and remote distances
> are 10 and 20 separately. This adds an extra parameter to the
> exiting complete_init_numa_distance() to generate the default
> distance map for this case.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  hw/core/numa.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/core/numa.c b/hw/core/numa.c
> index 510d096a88..fdb3a4aeca 100644
> --- a/hw/core/numa.c
> +++ b/hw/core/numa.c
> @@ -594,7 +594,7 @@ static void validate_numa_distance(MachineState *ms)
>      }
>  }
>  
> -static void complete_init_numa_distance(MachineState *ms)
> +static void complete_init_numa_distance(MachineState *ms, bool is_default)
>  {
>      int src, dst;
>      NodeInfo *numa_info = ms->numa_state->nodes;
> @@ -609,6 +609,8 @@ static void complete_init_numa_distance(MachineState *ms)
>              if (numa_info[src].distance[dst] == 0) {
>                  if (src == dst) {
>                      numa_info[src].distance[dst] = NUMA_DISTANCE_MIN;
> +                } else if (is_default) {
> +                    numa_info[src].distance[dst] = NUMA_DISTANCE_DEFAULT;
>                  } else {
>                      numa_info[src].distance[dst] = 
> numa_info[dst].distance[src];
>                  }
> @@ -716,13 +718,20 @@ void numa_complete_configuration(MachineState *ms)
>           * A->B != distance B->A, then that means the distance table is
>           * asymmetric. In this case, the distances for both directions
>           * of all node pairs are required.
> +         *
> +         * The default node pair distances, which are 10 and 20 for the
> +         * local and remote nodes separatly, are provided if user doesn't
> +         * specify any node pair distances.
>           */
>          if (ms->numa_state->have_numa_distance) {
>              /* Validate enough NUMA distance information was provided. */
>              validate_numa_distance(ms);
>  
>              /* Validation succeeded, now fill in any missing distances. */
> -            complete_init_numa_distance(ms);
> +            complete_init_numa_distance(ms, false);
> +        } else {
> +            complete_init_numa_distance(ms, true);
> +            ms->numa_state->have_numa_distance = true;
>          }
>      }
>  }
> -- 
> 2.23.0
>

With this patch we'll always generate a distance map when there's a numa
config now. Is there any reason a user would not want to do that? I.e.
should we still give the user the choice of presenting a distance map?
Also, does the addition of a distance map in DTs for compat machine types
matter?

Otherwise patch looks good to me.

Thanks,
drew