Re: [PATCH v2 0/8] x86/resctrl: Support for AMD Global (Slow) Memory Bandwidth Allocation

["Moger, Babu" <bmoger@amd.com>]

Hi Reinette,

On 5/1/2026 9:38 AM, Moger, Babu wrote:
> Hi Reinette,
> 
> On 4/30/2026 6:40 PM, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 4/30/26 4:04 PM, Moger, Babu wrote:
>>> Hi Reinette,
>>>
>>> On 4/29/2026 5:34 PM, Reinette Chatre wrote:
>>>> Hi Babu,
>>>>
>>>> On 4/23/26 6:41 PM, Babu Moger wrote:
>>>>>
>>>>> This series adds resctrl support for two new AMD memory-bandwidth
>>>>> allocation features:
>>>>>
>>>>>     - GMBA  - Global Memory Bandwidth Allocation (hardware name: 
>>>>> GLBE).
>>>>>               Bounds DRAM bandwidth for groups of threads that span
>>>>>               multiple L3 QoS domains, rather than being per-L3 
>>>>> like MBA.
>>>>>
>>>>>     - GSMBA - Global Slow Memory Bandwidth Allocation (hardware name:
>>>>>               GLSBE). The CXL.memory / slow-memory counterpart of 
>>>>> GMBA,
>>>>>               analogous to how SMBA relates to MBA.
>>>>>
>>>>> Both features share a new "NPS-node" control domain: a set of QoS (L3)
>>>>> domains grouped together and aligned to the system's NPS (Nodes Per
>>>>> Socket) BIOS configuration. Although the control domain is NPS-scoped,
>>>>> the underlying bandwidth-limit MSRs (MSR_IA32_GMBA_BW_BASE 0xc0000600,
>>>>> MSR_IA32_GSMBA_BW_BASE 0xc0000680) are instantiated per L3. 
>>>>> Programming
>>>>> a single control domain therefore requires writing the MSR on one CPU
>>>>> per L3 that the domain spans - a new pattern for resctrl. Patches 2/8
>>>>> and 3/8 introduce that infrastructure so the new resources can reuse
>>>>> it.
>>>>>
>>>>> The features are documented in:
>>>>>
>>>>>     AMD64 Zen6 Platform Quality of Service (PQOS) Extensions,
>>>>>     Publication # 69193 Revision 1.00, Issue Date March 2026
>>>>>
>>>>> available at https://bugzilla.kernel.org/show_bug.cgi?id=206537
>>>>>
>>>>> Series overview
>>>>> ---------------
>>>>>
>>>>> Patches 1-5 to enable GMBA:
>>>>>
>>>>>     1/8  x86,fs/resctrl: Add support for Global Bandwidth 
>>>>> Enforcement (GLBE)
>>>>>
>>>>>     2/8  x86/resctrl: Add RESCTRL_NPS_NODE scope for AMD NPS- 
>>>>> aligned domains
>>>>>          Add a new ctrl_scope value for resctrl resources whose 
>>>>> control
>>>>>          domain spans multiple L3s within an NPS node.
>>>>>
>>>>>     3/8  x86/resctrl: Update control MSRs per L3 for NPS-scoped 
>>>>> resources
>>>>>          Add resctrl_arch_update_nps(): builds a cpumask with one 
>>>>> CPU per
>>>>>          distinct L3 in the domain, then issues rdt_ctrl_update() via
>>>>>          smp_call_function_many() on that mask. Falls back to the full
>>>>>          domain mask if the scratch masks cannot be built. Route
>>>>>          resctrl_arch_update_domains() and 
>>>>> resctrl_arch_reset_all_ctrls()
>>>>>          through this helper when ctrl_scope == RESCTRL_NPS_NODE.
>>>>>
>>>>>     4/8  x86,fs/resctrl: Add the resource for Global Memory 
>>>>> Bandwidth Allocation
>>>>>          Register RDT_RESOURCE_GMBA in rdt_resources_all[] with
>>>>>          ctrl_scope=RESCTRL_NPS_NODE and schema_fmt=RANGE, add 
>>>>> commands to
>>>>>          discover feature details.
>>>>>
>>>>>     5/8  fs/resctrl: Add the documentation for Global Memory 
>>>>> Bandwidth Allocation
>>>>>          Add examples in Documentation/filesystems/resctrl.rst.
>>>>>
>>>>> Patches 6-8 to enable GSMBA in the same shape:
>>>>>
>>>>>     6/8  x86,fs/resctrl: Add support for Global Slow Memory 
>>>>> Bandwidth Allocation
>>>>>
>>>>>     7/8  x86,fs/resctrl: Add the resource for Global Slow Memory 
>>>>> Bandwidth Allocation
>>>>>          Register RDT_RESOURCE_GSMBA with ctrl_scope=RESCTRL_NPS_NODE.
>>>>>
>>>>>     8/8  fs/resctrl: Add the documentation for Global Slow Memory 
>>>>> Bandwidth Allocation
>>>>>          Add examples in Documentation/filesystems/resctrl.rst.
>>>>>
>>>>> Changes since v1
>>>>> ----------------
>>>>>     - Earlier sent RFC(v1) with Global Bandwidth Enforcement (GLBE) 
>>>>> and
>>>>>       Privilege Level Zero Association (PLZA). This series only 
>>>>> handles
>>>>>       Global Memory Bandwidth Allocation. Both the features are 
>>>>> sent separately.
>>>>>
>>>>>     - Documentation
>>>>>         * Fixed grammar in the GMBA / GSMBA sections of resctrl.rst.
>>>>>         * Added examples to update GMBA and GSMBA in resctrl.rst 
>>>>> documentation.
>>>>>
>>>>>     - Major changes are releated to RESCTRL_NPS_NODE scope handling.
>>>>>
>>>>>     - Commit messages
>>>>>         * Reworked the changelogs in all the patches.
>>>>>
>>>>> Previous Revisions:
>>>>> v1 : https://lore.kernel.org/lkml/ 
>>>>> cover.1769029977.git.babu.moger@amd.com/
>>>>
>>>> What are your expectations from this submission? From what I can 
>>>> tell this ignores
>>>> v1 feedback in several ways:
>>>> - It introduces two new resources, GMBA and GSMBA, when the previous 
>>>> discussion agreed that
>>>>     these are not actually new resources but instead new controls 
>>>> for the existing MBA/SMBA resources.
>>>> - It does not mention or attempt to address dependency on new 
>>>> resource schema descriptions [1]
>>>>     to support user space in understanding how to interact with the 
>>>> new GMBA/GSMBA controls but
>>>>     instead defers that to a snippet in the documentation that user 
>>>> space needs to
>>>>     parse to know this control operates at multiples of 1GB/s.
>>>>
>>>> Apart from ignoring v1 feedback this new version appears to 
>>>> complicate user interface even more
>>>> since now it is possible for there to be a single control that may 
>>>> operate at different scopes but from
>>>> what I can tell there is nothing that helps user understand whether, 
>>>> for example, domain "0" means
>>>> the whole system or a NUMA node?
>>>>
>>>> We have discussed several times now how resctrl interface needs to 
>>>> be enhanced to support
>>>> this and other upcoming features from Intel, RISC-V, Arm MPAM, and 
>>>> NVidia. It is thus
>>>> unexpected that this submission ignores all the previous discussions.
>>>
>>> I think there may be some misunderstanding on this topic.
>>>
>>> Yes, we discussed it earlier. It depends on other requirements 
>>> (region-aware aspects), so I assumed it would be handled by someone 
>>> with full context and addressed as a separate feature. I didn’t have 
>>> complete visibility into all the requirements.
>>
>> Please read https://lore.kernel.org/lkml/06a237bd- 
>> c370-4d3f-99de-124e8c50e711@intel.com/ again.
>>
>> You should have complete visibility into the foundation of this work 
>> since one of the
>> primary goals is to address the resctrl interface breakage that came 
>> with the initial AMD
>> support for MBA that resctrl has been living with until now.
>>
>> With this series you completely disregard attempts to support users in 
>> understanding
>> how to interact with the schemata file and instead introduce *another* 
>> obfuscated control. I
>> will not support this.
>>
>> Also, no, this does not depend on region-aware work. Needing to 
>> support multiple controls for
>> a single resource is independent from region-aware.
>>
>>>> Since there are so many dependencies on the new schema format 
>>>> support I am prioritizing this
>>>> and created a PoC that I am currently refining and hope to share 
>>>> soon. We can collaborate on this
>>>> to ensure that it provides a good foundation for the GMBA and GSMBA 
>>>> support.
>>>
>>> That is good to know. Let me know when you are ready.
>>>
>>> Could you please share which parts of the feature (e.g., Part 1, Part 
>>> 2, etc.) you are planning to cover in your PoC?
>>
>> All three parts mentioned in https://lore.kernel.org/lkml/06a237bd- 
>> c370-4d3f-99de-124e8c50e711@intel.com/
>>
>> This does not address all the features discussed, for example it does 
>> not support emulated controls,
>> but I hope it is enough of a foundation to build on.
> 
> Please share your code when you are ready. I can build GMB and GSMBA on 
> top of your patches. Hopefully, I can reuse some of the code from this 
> series.

I didn’t see your acknowledgment on my previous note, so I wanted to 
follow up to ensure we’re aligned.

Just to confirm—are you planning to share your PoC?

My understanding is that I would build GMB/GSMBA on top of your patches. 
Please let me know if that’s correct.

There’s no urgency on the patches at this point; I mainly wanted to get 
some clarity on the plan.

Thanks,
Babu