[Xen-devel] Re: Some Problems about Xen Numa support $B!*(B

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

Probably Linux lets yuou specify NUMA topology on the command line, or something like that, and the loop you point out is inherited from that support.

 -- Keir

On 27/5/08 02:02, "李亚琼" <liyaq04@xxxxxxxxxx> wrote:

> Hi，All
>          I am reading the concerned source code of Numa support in Xen source tree. I have been puzzled with the initialization of Numa support. During the initialization, the function ‘acpi_scan_nodes’ is called to scan the information about numa system. It converts some temporary variables into final variables, such as nodes -> node_data。My puzzles locate in the last lines of this function:
> int __init acpi_scan_nodes(u64 start, u64 end)
> {
> ………
>          /* Finally register nodes */
>          for_each_node_mask(i, nodes_parsed)
>                   setup_node_bootmem(i, nodes[i].start, nodes[i].end);
>          for (i = 0; i < NR_CPUS; i++) { 
>                   if (cpu_to_node[i] == NUMA_NO_NODE)
>                            continue;
>                   if (!node_isset(cpu_to_node[i], nodes_parsed))
>                            numa_set_node(i, NUMA_NO_NODE);
>          }
>         numa_init_array();
>         return 0;
> }
> According my study, the variable ‘cpu_to_node’ has a unified value—NUMA_NO_NODE before this codes being executed. So, the ‘for loop’ will have no effect. Is it correct?
> The following function ‘numa_init_array’ will be called. Its source code is here:
> void __init numa_init_array(void)
> {
>          int rr, i;
>          /* There are unfortunately some poorly designed mainboards around
>            that only connect memory to a single CPU. This breaks the 1:1 cpu->node
>            mapping. To avoid this fill in the mapping for all possible
>            CPUs, as the number of CPUs is not known yet. 
>            We round robin the existing nodes. */
>          rr = first_node(node_online_map);
>          for (i = 0; i < NR_CPUS; i++) {
>                   if (cpu_to_node[i] != NUMA_NO_NODE)
>                            continue;
>                  numa_set_node(i, rr);
>                   rr = next_node(rr, node_online_map);
>                   if (rr == MAX_NUMNODES)
>                            rr = first_node(node_online_map);
>          }
>  
> }
> I don’t understand why it is called here. I think it should be called after cpu_to_node being initialized with correct value.
> Thanks a lot!
>  
> -Techie
>  
>  




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