[PATCH] powerpc/numa: Fix topology_physical_package_id() on pSeries

[Cédric Le Goater]

On 3/15/21 4:12 PM, Daniel Henrique Barboza wrote:
> 
> 
> On 3/12/21 11:31 AM, Cédric Le Goater wrote:
>> Initial commit 15863ff3b8da ("powerpc: Make chip-id information
>> available to userspace") introduce a cpu_to_chip_id() routine for the
>> PowerNV platform using the "ibm,chip-id" property to query the chip id
>> of a CPU. But PAPR does not specify such a property and the node id
>> query is broken.
>>
>> Use cpu_to_node() instead which guarantees to have a correct value on
>> all platforms, PowerNV an pSeries.
> 
> It is worth mentioning that that this patch will change how
> topology_physical_package_id() represents in a QEMU guest. Right now, ibm,chip-id
> in QEMU is matching the socket-id. After this patch, topology_physical_package_id()
> will now match the NUMA id of the CPU.

yes. I should have added some more background. 

LPARs are impacted by the use of ibm,chip-id because the property 
does not exist under PowerVM and the topology-id in sysfs is always
-1 even if NUMA nodes are defined.

Under QEMU/KVM, ibm,chip-id is badly calculated when using uncommon 
SMT configuration. This leads to a bogus topology-id value being 
exported in sysfs.

The use of cpu_to_node() guarantees to have a correct NUMA node id 
under both environments QEMU/KVM and PowerVM.

On the PowerNV platform, the numa node id returned by cpu_to_node() 
is computed from the "ibm,associativity" property of the CPU. Its 
value is built from the OPAL chip id and is equivalent to ibm,chip-id. 

May be I should rephrase the commit log in a v2 ?

C.

 
> Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> Tested-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> 
>>
>> Cc: Nathan Lynch <nathanl at linux.ibm.com>
>> Cc: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
>> Cc: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>
>> Signed-off-by: Cédric Le Goater <clg at kaod.org>
>> ---
>>   arch/powerpc/include/asm/topology.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
>> index 3beeb030cd78..887c42a4e43d 100644
>> --- a/arch/powerpc/include/asm/topology.h
>> +++ b/arch/powerpc/include/asm/topology.h
>> @@ -123,7 +123,7 @@ static inline int cpu_to_coregroup_id(int cpu)
>>   #ifdef CONFIG_PPC64
>>   #include <asm/smp.h>
>>   -#define topology_physical_package_id(cpu)    (cpu_to_chip_id(cpu))
>> +#define topology_physical_package_id(cpu)    (cpu_to_node(cpu))
>>     #define topology_sibling_cpumask(cpu)    (per_cpu(cpu_sibling_map, cpu))
>>   #define topology_core_cpumask(cpu)    (cpu_cpu_mask(cpu))
>>