Re: [RFC v2] arm,x86,fs/resctrl: Generic schema description Proof of Concept

[Chen, Yu C]

Hi Reinette,

Thank you very much for providing this version,

On 8/4/2026 1:26 PM, Reinette Chatre wrote:

> - Only "SAMPLE" code provided for x86 to demonstrate emulated controls.

> - Add relationships between controls. For example, cannot set "MIN" control
>    value to be larger than "MAX. Unclear how to do this in resctrl fs when
>    considering that the relationship may span between enabled and disabled
>    controls. This is potentially something that needs to be managed by architecture
>    and thus potentially without a consistent failure to user space.
>                                                                                  

I have tested this version, and it exhibits the expected
behavior according to my understanding:

The following is the legacy schemata:
[root@ resctrl]# cat schemata
            MB:0=100;1=100;2=100;3=100

and the following is the native schemata:
[root@ resctrl]# echo native > /sys/fs/resctrl/info/MB/control_mode
[root@ resctrl]# cat schemata
MB_REGION0_MAX:0=200;1=200;2=200;3=200
MB_REGION0_MIN:0=1;1=1;2=1;3=1

I have a minor question I'd like to confirm:

item 1.
In legacy mode, we intend to always let the "native" controller
emulate the "legacy" controller - at least for the region‑aware
RDT case.
Q1: Is this understanding correct?

item 2.
In commit fbed64f80515 ("x86/resctrl: SAMPLE: Emulated controls"),
during resctrl initialization, __get_mem_config_intel() clears
the legacy controller's hw_ctrl->msr_update to NULL, and sets
its emulation controllers in hw_ctrl->r_ctrl.emulated_by to
the region-aware related controllers. So legacy controller is
emulated by region-aware controllers.

item 3.
In resctrl_arch_control_mode_set(), when switching to "legacy"
mode, the legacy controller is set to:
hw_ctrl->msr_update = update_temporary_legacy_MB;
while the emulating controller is set to NULL:
hw_ctrl->msr_update = NULL;
That means, the emulated controllers will not take effect.

Q2:Does item 3 contradict item 1?


thanks,
Chenyu