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

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Message-ID: <87tsy0kgwy.fsf@stealth>
Date: Mon, 08 Dec 2025 17:43:57 +0000
From: Punit Agrawal <punit.agrawal@....qualcomm.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: Punit Agrawal <punit.agrawal@....qualcomm.com>,
        James Morse
 <james.morse@....com>, Ben Horgan <ben.horgan@....com>,
        <amitsinght@...vell.com>, <baisheng.gao@...soc.com>,
        <baolin.wang@...ux.alibaba.com>, <bobo.shaobowang@...wei.com>,
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Subject: Re: [PATCH v6 00/34] arm_mpam: Add basic mpam driver

Hi Reinette,

Reinette Chatre <reinette.chatre@...el.com> writes:

> Hi Punit,
>
> On 12/5/25 5:08 AM, Punit Agrawal wrote:
>> James Morse <james.morse@....com> writes:
>>> On 03/12/2025 11:21, Punit Agrawal wrote:
>>>> Ben Horgan <ben.horgan@....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.

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