Re: [PATCH 3/6] x86/numa: define numa_init_array() conditional on CONFIG_NUMA

[Dave Hansen]

On 2/24/19 4:34 AM, Pingfan Liu wrote:
> +#ifdef CONFIG_NUMA
>  /*
>   * There are unfortunately some poorly designed mainboards around that
>   * only connect memory to a single CPU. This breaks the 1:1 cpu->node
> @@ -618,6 +619,9 @@ static void __init numa_init_array(void)
>  		rr = next_node_in(rr, node_online_map);
>  	}
>  }
> +#else
> +static void __init numa_init_array(void) {}
> +#endif

What functional effect does this #ifdef have?

Let's look at the code:

> static void __init numa_init_array(void)
> {
>         int rr, i;
> 
>         rr = first_node(node_online_map);
>         for (i = 0; i < nr_cpu_ids; i++) {
>                 if (early_cpu_to_node(i) != NUMA_NO_NODE)
>                         continue;
>                 numa_set_node(i, rr);
>                 rr = next_node_in(rr, node_online_map);
>         }
> }

and "play compiler" for a bit.

The first iteration will see early_cpu_to_node(i)==1 because:

static inline int early_cpu_to_node(int cpu)
{
        return 0;
}

if CONFIG_NUMA=n.

In other words, I'm not sure this patch does *anything*.