Re: [PATCH v6 00/34] arm_mpam: Add basic mpam driver

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Punit,

On 12/8/25 9:43 AM, Punit Agrawal wrote:
> Hi Reinette,
> 
> Reinette Chatre <reinette.chatre@intel.com> writes:
> 
>> Hi Punit,
>>
>> On 12/5/25 5:08 AM, Punit Agrawal wrote:
>>> James Morse <james.morse@arm.com> writes:
>>>> On 03/12/2025 11:21, Punit Agrawal wrote:
>>>>> Ben Horgan <ben.horgan@arm.com> writes:
>>>>>> On 11/24/25 15:21, Punit Agrawal wrote:
>>
>>>>>>> The platform has MSCs attached
>>>>>>> to shared L2 caches which are being skipped during later stages of
>>>>>>> initialisation. IIUC, the L2 MSCs' limitations stems from the
>>>>>>> assumptions in the resctrl interface.
>>>>>>
>>>>>> What in particualar is being skipped?
>>>>
>>>>> The registration of the discovered MSCs with resctrl and subsequent
>>>>> exposing it to the user.
>>>>
>>>> resctrl's 'L2' support is limited to the CPOR bitmap.
>>>> If you have controls, there is no resctrl 'event' that can exposed them.
>>>> (the problem being they all have 'L3' in the name!)
>>>
>>>>>>> I was wondering if there are any patches available to relax these
>>>>>>> limitations?
>>>
>>>> Knowing which property it is will help - but some of these things are checked
>>>> to match resctrl's ABI. They can't necessarily be relaxed without breaking
>>>> user-space.
>>>
>>> This platform has portion, capacity and priority partitioning, as well
>>> as memory bandwidth and cache storage monitoring. The MPAM code seems to
>>> correctly parse the properties.
>>>
>>> But as you point out, the resctrl 'L2' support doesn't have anything
>>> other than CPOR bitmap yet. Have you looked at what's needed to extend
>>> resctrl to support some of the others?
>>
>> Please see [1] for a summary of ideas on how resctrl can support multiple
>> controls. Nothing is final, please do add your ideas and requirements.
>>
>> There are a couple of opens not included in the summary. If interested
>> [2] is where a lot of discussion happened that prompted the need for
>> a summary.
> 
> Thanks a lot for the pointers.
> 
> Let me catch up with what's already discussed and raise any points that
> are not clear / need refining.

Please do. There are already a few known open issues. I plan to raise awareness
of these discussions (and the (so far known) sticky points still left to resolve) during
the resctrl session at LPC:
https://lpc.events/event/19/contributions/2093/

I am attending LPC remotely though so I hope increased awareness will result in more traffic
to [1] to help us get this right.

Reinette


> 
>>
>> Reinette
>>
>> [1] https://lore.kernel.org/lkml/aPtfMFfLV1l%2FRB0L@e133380.arm.com/
>> [2] https://lore.kernel.org/lkml/aNFliMZTTUiXyZzd@e133380.arm.com/