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Subject: Re: [RFC PATCH 1/2] powerpc/numa: Introduce logical numa id
To: Nathan Lynch <nathanl@linux.ibm.com>
References: <20200731111916.243569-1-aneesh.kumar@linux.ibm.com>
 <87pn83ytet.fsf@linux.ibm.com>
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Message-ID: <324611f7-fdaf-f83c-7159-977488aa7ce7@linux.ibm.com>
Date: Fri, 7 Aug 2020 10:32:13 +0530
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On 8/7/20 9:54 AM, Nathan Lynch wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
>> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
>> index e437a9ac4956..6c659aada55b 100644
>> --- a/arch/powerpc/mm/numa.c
>> +++ b/arch/powerpc/mm/numa.c
>> @@ -221,25 +221,51 @@ static void initialize_distance_lookup_table(int nid,
>>   	}
>>   }
>>   
>> +static u32 nid_map[MAX_NUMNODES] = {[0 ... MAX_NUMNODES - 1] =  NUMA_NO_NODE};
> 
> It's odd to me to use MAX_NUMNODES for this array when it's going to be
> indexed not by Linux's logical node IDs but by the platform-provided
> domain number, which has no relation to MAX_NUMNODES.


I didn't want to dynamically allocate this. We could fetch 
"ibm,max-associativity-domains" to find the size for that. The current 
code do assume  firmware group id to not exceed MAX_NUMNODES. Hence kept 
the array size to be MAX_NUMNODEs. I do agree that it is confusing. May 
be we can do #define MAX_AFFINITY_DOMAIN MAX_NUMNODES?



> 
>> +
>> +int firmware_group_id_to_nid(int firmware_gid)
>> +{
>> +	static int last_nid = 0;
>> +
>> +	/*
>> +	 * For PowerNV we don't change the node id. This helps to avoid
>> +	 * confusion w.r.t the expected node ids. On pseries, node numbers
>> +	 * are virtualized. Hence do logical node id for pseries.
>> +	 */
>> +	if (!firmware_has_feature(FW_FEATURE_LPAR))
>> +		return firmware_gid;
>> +
>> +	if (firmware_gid ==  -1)
>> +		return NUMA_NO_NODE;
>> +
>> +	if (nid_map[firmware_gid] == NUMA_NO_NODE)
>> +		nid_map[firmware_gid] = last_nid++;
> 
> This should at least be bounds-checked in case of domain numbering in
> excess of MAX_NUMNODES. Or a different data structure should be used?
> Not sure.
> 
> I'd prefer Linux's logical node type not be easily interchangeable with
> the firmware node/group id type. The firmware type could be something
> like:
> 
> struct affinity_domain {
> 	u32 val;
> };
> typedef struct affinity_domain affinity_domain_t;
> 
> with appropriate accessors/APIs.
> 

That is a good idea. Will use this.

-aneesh