Re: [RESEND PATCH v4 04/15] fs/resctrl: Introduce kernel mode (kmode) data structures

[Babu Moger <babu.moger@amd.com>]

Hi Reinette,

On 8/12/26 18:28, Reinette Chatre wrote:
> Hi Babu,
> 
> On 8/12/26 12:58 PM, Moger, Babu wrote:
>> On 8/10/2026 10:03 PM, Reinette Chatre wrote:
>>> On 7/7/26 2:50 PM, Babu Moger wrote:
> 
>>>> can report what is active or what the platform supports.
>>>>
>>>> Introduce enum resctrl_kernel_mode:
>>>>     - INHERIT_CTRL_AND_MON: Kernel work inherits allocation and monitoring
>>>>       from the user task (current behavior).
>>>
>>> The issue with this "combination" mode becomes obvious in patch 7. I also
>>> see that sashiko hinted at this issue but I am not able to see from your response
>>> what the plan is to address this. As highlighted by patch 7 and sashiko the
>>> "allocation" and "monitoring" features of a system are independent - a system
>>> need not support/enable both. This should be easy to reproduce by, for example,
>>> booting a system with needed rdt= options disabling allocation or monitoring
>>> features.
>>>
>>> I think it will be unexpected to a user on an allocation-only system to
>>> see interface like:
>>>
>>>    # cat info/kernel_mode
>>>     [inherit_ctrl_and_mon]
>>>     global_assign_ctrl_inherit_mon_per_cpu:group=uninitialized
>>>     global_assign_ctrl_assign_mon_per_cpu:group=uninitialized
>>>
>>> Should it not rather be, for example:
>>>    # cat info/kernel_mode
>>>     [inherit_ctrl]
>>>     global_assign_ctrl_per_cpu:group=uninitialized
>>>
>>> Similarly the user input would not need to provide a monitor group when system
>>> only supports allocation.
>>
>> Ok. Yea. We need to separate control and monitor separately.
>>
>>
>> How about something like this?
>>
>>   # cat info/kernel_mode
>>     [ctrl=inherit,mon=inherit]
>>     ctrl=assign,mon=inherit:group=uninitialized
>>     ctrl=assign,mon=assign:group=uninitialized
>>     ctrl=inherit,mon=assign:group=uninitialized
>>
>> If allocation(ctrl) is only supported.
>>
>>   # cat info/kernel_mode
>>     [ctrl=inherit]
>>     ctrl=assign:group=uninitialized
>>
>> If monitor (mon) is only supported.
>>
>>   # cat info/kernel_mode
>>     [mon=inherit]
>>     mon=assign:group=uninitialized
>>
>>
> 
> Please always keep in mind all the requirements and use cases we learned about
> during and after RFC v1 of this work.
> 
> For example, we already know that "per group" assignment is something resctrl
> needs to be ready for. Consider the example in
> https://lore.kernel.org/lkml/aYyxAPdTFejzsE42@e134344.arm.com/
> 
> There may even be "per task" assignment in the future.

Yes. That is correct.

> 
> Constraining this feature to PLZA will make it harder to enable the capabilities
> that we know resctrl need to support in the future.
> 
> This is how we originally landed on the "global" assignment distinction
> (https://lore.kernel.org/lkml/2ab556af-095b-422b-9396-f845c6fd0342@intel.com/)
> "global assignment" should be kept or replaced with a solution that continues to
> prepare resctrl for these other capabilities.

Yes. Makes sense.

> 
> I am not able to see how resctrl could support "per group" assignment with the
> interface you propose above. If I am missing this, please highlight the solution.
> 
> resctrl may need to explicitly split kernel mode from kernel mode properties. For
> example, below shows an "assign_global_enable_per_cpu" as the kernel mode, now with three
> properties:
> - "ctrl" - could be "assign" or "inherit"
> - "mon" - could be "assign" or "inherit"
> - "group" - required if "ctrl" or "mon" is set to "assign"

ok.


> 
>     # cat info/kernel_mode
>     [inherit]
>     assign_global_enable_per_cpu:ctrl=assign;mon=assign;group=uninitialized

Shouldn't this be like below when default is inherit?

# cat info/kernel_mode
[inherit]
assign_global_enable_per_cpu


When the default changes to assign_global_enable_per_cpu:

# cat info/kernel_mode
inherit 
[assign_global_enable_per_cpu:ctrl=assign;mon=assign;group=ctrl_mon1//]

Display the second mode with properties only when group is associated 
with it?

# cat info/kernel_mode
inherit
[assign_global_enable_per_cpu:mon=assign;group=ctrl1/mon1/]


> 
> When resctrl needs to support "per-group" assignment "kernel_mode" could contain
> below with supporting documentation noting which per-resource group files will
> appear when "assign_per_group" is selected that user space can use to manage
> the assignments.
> 
>     # cat info/kernel_mode
>     [inherit]
>     assign_per_group
> 

I know it is future. What could be difference between 
assign_global_enable_per_cpu and assign_per_group?

Thanks

Babu