[PATCH v2 1/3] powerpc/numa: Introduce logical numa id

[Aneesh Kumar K.V]

On 8/17/20 4:29 PM, Srikar Dronamraju wrote:
> * Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com> [2020-08-17 16:02:36]:
> 
>> We use ibm,associativity and ibm,associativity-lookup-arrays to derive the numa
>> node numbers. These device tree properties are firmware indicated grouping of
>> resources based on their hierarchy in the platform. These numbers (group id) are
>> not sequential and hypervisor/firmware can follow different numbering schemes.
>> For ex: on powernv platforms, we group them in the below order.
>>
>>   *     - CCM node ID
>>   *     - HW card ID
>>   *     - HW module ID
>>   *     - Chip ID
>>   *     - Core ID
>>
>> Based on ibm,associativity-reference-points we use one of the above group ids as
>> Linux NUMA node id. (On PowerNV platform Chip ID is used). This results
>> in Linux reporting non-linear NUMA node id and which also results in Linux
>> reporting empty node 0 NUMA nodes.
>>
>> This can  be resolved by mapping the firmware provided group id to a logical Linux
>> NUMA id. In this patch, we do this only for pseries platforms considering the
>> firmware group id is a virtualized entity and users would not have drawn any
>> conclusion based on the Linux Numa Node id.
>>
>> On PowerNV platform since we have historically mapped Chip ID as Linux NUMA node
>> id, we keep the existing Linux NUMA node id numbering.
> 
> I still dont understand how you are going to handle numa distances.
> With your patch, have you tried dlpar add/remove on a sparsely noded machine?
> 

We follow the same steps when fetching distance information. Instead of 
using affinity domain id, we now use the mapped node id. The relevant 
hunk in the patch is

+	nid = affinity_domain_to_nid(&domain);

  	if (nid > 0 &&
-		of_read_number(associativity, 1) >= distance_ref_points_depth) {
+	    of_read_number(associativity, 1) >= distance_ref_points_depth) {
  		/*
  		 * Skip the length field and send start of associativity array
  		 */

I haven't tried dlpar add/remove. I don't have a setup to try that. Do 
you see a problem there?

-aneesh