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

Reinette Chatre
2026-04-09T20:50:45Z

Hi Babu,

On 4/9/26 11:05 AM, Moger, Babu wrote:
> On 4/9/2026 12:26 PM, Reinette Chatre wrote:
>> 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.
>

ok. Could you please return the courtesy of providing feedback on the
suggestion you are responding to and also include the motivation why your
suggestion is the better option?

Reinette