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

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

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.

Thanks
Babu