Re: [RFC PATCH v2 1/5] arm_mpam: resctrl: Pick classes for use as mbm counters

[Ben Horgan]

Hi Shaopeng,

On 3/27/26 02:53, Shaopeng Tan (Fujitsu) wrote:
> Hello Ben,
> 
> 
>> resctrl has two types of counters, NUMA-local and global. MPAM can only
>> count global either using MSC at the L3 cache or in the memory controllers.
>> When global and local equate to the same thing continue just to call it
>> global.
>>
>> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
>> Tested-by: Zeng Heng <zengheng4@xxxxxxxxxx>
>> Reviewed-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
>> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
>> Signed-off-by: James Morse <james.morse@xxxxxxx>
>> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>

> 
> There are environments with multiple L3 caches within a single NUMA node.
> In this case, mbm_total will be the sum of traffic from all caches within that NUAM node.
> Is my understanding correct?

No, currently you only get mbm_total if there is single L3 cache and a single corresponding NUMA node. Rather than
adding partial support by summing across numa nodes we plan to add support for memory bandwidth monitoring with NUMA
node scope.

Thanks,

Ben

> 
> 
> Best regards,
> Shaopeng TAN