Re: [PATCH v2 00/16] fs,x86/resctrl: Add kernel-mode (e.g., PLZA) support to the resctrl subsystem

Moger, Babu
2026-04-09T18:05:54Z

Hi Reinette,

On 4/9/2026 12:26 PM, Reinette Chatre wrote:
>
> Hi Babu,
>
> On 4/9/26 10:19 AM, Moger, Babu wrote:
>> On 4/8/2026 6:41 PM, Reinette Chatre wrote:
>
>>> When the user switches to either "global_assign_ctrl_inherit_mon_per_cpu" or
>>> 'global_assign_ctrl_assign_mon_per_cpu" then "info/kernel_mode_assignment" is created
>>> (or made visible to user space) and is expected to point to default group.
>>> User can change the group using "info/kernel_mode_assignment" at this point.
>>>
>>> If the current scenario is below ...
>>>     # cat info/kernel_mode
>>>     [global_assign_ctrl_inherit_mon_per_cpu]
>>>     inherit_ctrl_and_mon
>>>     global_assign_ctrl_assign_mon_per_cpu
>>>
>>> ... then "info/kernel_mode_assignment" will exist but what it should contain if
>>> user switches mode at this point may be up for discussion.
>>>
>>> option 1)
>>> When user switches mode to "global_assign_ctrl_assign_mon_per_cpu" then
>>> the resource group in "info/kernel_mode_assignment" is reset to the
>>> default group and all CPUs PLZA state reset to match. The kernel_mode_cpus
>>> and kernel_mode_cpuslist files become visible in default resource group
>>> and they contain "all online CPUs".
>>>
>>> option 2)
>>> When user switches mode to "global_assign_ctrl_assign_mon_per_cpu" then
>>> the resource group in "info/kernel_mode_assignment" is kept and all
>>> CPUs PLZA state set to match it while also keeping the current
>>> values of that resource group's kernel_mode_cpus and kernel_mode_cpuslist
>>> files.
>>>
>>> I am leaning towards "option 1" to keep it consistent with a switch from
>>> "inherit_ctrl_and_mon" and being deterministic about how a mode is started with
>>
>> Yes. The "option 1" seems appropriate.
>>
>>> a clean slate. What are your thoughts? What would be use case where a user would
>>> want to switch between "global_assign_ctrl_inherit_mon_per_cpu" and
>>> "global_assign_ctrl_assign_mon_per_cpu" to just switch rmid_en on and off?
>>
>>
>> This is a bit tricky.
>>
>> Currently, our requirement is to have a CTRL_MON group for
>> global_assign_ctrl_inherit_mon_per_cpu. In this scenario, we use the
>> group’s CLOSID for PLZA configuration, and RMID is not used (rmid_en
>> = 0) when setting up PLZA.
>>
>> Our requirement is also to have a CTRL_MON/MON group for
>> global_assign_ctrl_assign_mon_per_cpu. In this case as well, the
>> group’s CLOSID and RMID (rmid_en = 1) both are used configure PLZA.
>
> ah, right. Good catch.
>
>>
>> Actually, we should not allow these changes from
>> global_assign_ctrl_inherit_mon_per_cpu to
>> global_assign_ctrl_assign_mon_per_cpu or visa versa.
>
> resctrl could allow it but as part of the switch it resets the "kernel mode group" to
> be the default group every time? This would be the "option 1" above.

Other options.

Allow global_assign_ctrl_inherit_mon_per_cpu ->
global_assign_ctrl_assign_mon_per_cpu. As part of the switch, reset the
"kernel mode group" to the default group.

Allow global_assign_ctrl_assign_mon_per_cpu ->
global_assign_ctrl_inherit_mon_per_cpu. In this case switch
to CTRL_MON/MON -> CTRL_MON.

Thanks
Babu

>
> Reinette
>
>