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

Moger, Babu
2026-04-21T22:04:32Z

Hi Reinette,

On 4/21/2026 3:57 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 4/21/26 11:19 AM, Babu Moger wrote:
>> On 4/21/26 12:35, Reinette Chatre wrote:
>>> On 4/21/26 9:46 AM, Babu Moger wrote:
>>>> On 4/21/26 11:15, Reinette Chatre wrote:
>>>>> On 4/21/26 8:08 AM, Babu Moger wrote:
>
>
>>>>>>
>>>>>> # echo "global_assign_ctrl_assign_mon_per_cpu:group=ctrl1/mon1/
>>>>>>
>>>>>> Why do we still need to keep the "inherit_ctrl_and_mon"?  By default all the groups in the system falls in this category it is not plza enabled group.
>
> Here you question why "inherit_ctrl_and_mon" is needed ...
>
>>>>>>
>>>>>>
>>>>>> System boots up with following options if PLZA is supported.
>>>>>>
>>>>>> # cat info/kernel_mode
>>>>>>         global_assign_ctrl_assign_mon_per_cpu
>>>>>>         global_assign_ctrl_inherit_mon_per_cpu
>>>>>>
>>>>>> No groups are associated with kernel mode at this point.
>>>>>
>>>>> To me it seems useful to be clear to user space on what the current mode is. If I understand correctly
>>>>> above default scenario essentially means "inherit_ctrl_and_mon" but instead of adding it to this file
>>>>> we will need to add documentation that describes to user space how this file should be interpreted.
>>>>> It seems easier to me to just be clear via info/kernel_mode itself on what the current active mode is?
>>>>>
>>>>> I think something like below will be more intuitive and not need much additional
>>>>> documentation to understand (I am just adding the "uninitialized" as an example to match text
>>>>> printed in schemata file during pseudo-locking ... even if there is a group named "uninitialized"
>>>>> the lack of "/" could be used to make it clear what this means?):
>>>>>
>>>>>      # cat info/kernel_mode
>>>>>      [inherit_ctrl_and_mon]
>>>>>      global_assign_ctrl_assign_mon_per_cpu:group=uninitialized
>>>>>      global_assign_ctrl_inherit_mon_per_cpu:group=uninitialized
>>>>>
>
> Above I share considerations when thinking whether to keep "inherit_ctrl_and_mon" or not ...
>
>>>>
>>>> Sounds ok to me.
>
> ... to which you seem to agree ...
>
>>>>
>>>>
>>>>> I also think an interface like this would be simpler for user space to use as it (user space) switches
>>>>> between PLZA capable and non-PLZA capable systems since user space need not associate existence of
>>>>> the file with some kernel mode state in addition to actual content of the file when it does exist.
>
>
> ... more considerations from me when thinking whether to keep "inherit_ctrl_and_mon" or not ...

My bad. My only motivation was to keep the mode listing display consistent.

That said, I agree we need to support this. Without it, we won’t be able
to move the group from PLZA to non-PLZA.

# cat info/kernel_mode
inherit_ctrl_and_mon:
global_assign_ctrl_assign_mon_per_cpu:group=uninitialized
[global_assign_ctrl_assign_mon_per_cpu]:group=ctrl1/mon1/

# echo "inherit_ctrl_and_mon:group=ctrl1/mon1/" > info/kernel_mode

# cat info/kernel_mode
inherit_ctrl_and_mon:
global_assign_ctrl_assign_mon_per_cpu:group=uninitialized
[global_assign_ctrl_assign_mon_per_cpu]:group=uninitialized

Thanks
Babu