linux-kernel - Re: [PATCH v13 00/27] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <877642a9-cef0-4b80-9053-3ecace9326ed@intel.com>
Date: Thu, 22 May 2025 09:33:33 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....com>, Peter Newman <peternewman@...gle.com>
CC: "Moger, Babu" <bmoger@....com>, <corbet@....net>, <tony.luck@...el.com>,
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Subject: Re: [PATCH v13 00/27] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

Hi Babu,

On 5/22/25 8:44 AM, Moger, Babu wrote:
> On 5/21/25 18:03, Reinette Chatre wrote:

...

>> This is why I proposed in [3] that the name of the mode reflects how user can interact
>> with the system. Instead of one "mbm_cntr_assign" mode there can be "mbm_cntr_event_assign"
>> that is used for ABMC and "mbm_cntr_group_assign" that is used for soft-ABMC. The mode should
>> make it clear what the system is capable of wrt counter assignments.
> 
> Yes, that makes sense. Perhaps we can also simplify it further:
> 
> # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode:
> [mbm_cntr_evt_assign] <- for ABMC
>  mbm_cntr_grp_assign  <- for soft-ABMC

Looks good to me. Thank you.

>> Considering this the interface should be clear:
>> num_mbm_cntrs: reflects the number of counters in each domain that can be assigned. In
>> "mbm_cntr_event_assign" this will be the number of counters that can be assigned to 
>> each event within a monitoring group, in "mbm_cntr_group_assign" this will be the number
>> of counters that can be assigned to entire monitoring groups impacting all MBM events.
>>
>> mbm_L3_assignments: manages the counter assignment in each group. When user knows the mode
>> is "mbm_cntr_event_assign"/"mbm_cntr_group_assign" then it should be clear to user space how the
>> interface behaves wrt assignment, no surprises of multiple events impacted when
>> assigning/unassigning single event.
>>
>> For soft-ABMC I thus find it most intuitive for num_mbm_cntrs to be the exact number
>> of "active" RMIDs that the system can support *and* changing the name of the modes
>> to help user interpret num_mbm_cntrs.
> 
> Sure. The option A: fits well here then.
> 
>  Option A (counters are RMIDs):
>  # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
>  0=31;1=31

Thank you for considering.

Please add the requirements from this discussion to your running list. Also please keep in mind
how soft-ABMC intends to use the interfaces created by this work so that the documentation that
accompanies the ABMC support in this series leaves enough "wiggle room" for soft-ABMC to be built on top.

>>> [1] https://lore.kernel.org/lkml/CALPaoChSzzU5mzMZsdT6CeyEn0WD1qdT9fKCoNW_ty4tojtrkw@mail.gmail.com/
>>
>> Reinette
>>
>> [2] https://lore.kernel.org/lkml/b9e48e8f-3035-4a7e-a983-ce829bd9215a@intel.com/
>> [3] https://lore.kernel.org/lkml/b3babdac-da08-4dfd-9544-47db31d574f5@intel.com/
>>
> 

Reinette