Re: [PATCH v1] fs/resctrl: Add missing kconfig entry for CONFIG_RESCTRL_ASSIGN_FIXED

[Reinette Chatre]

Hi Ben,

On 1/15/26 7:46 AM, Ben Horgan wrote:
> Hi Reinette,
> 
> On 1/15/26 15:37, Reinette Chatre wrote:
>> Hi Ben,
>>
>> On 1/15/26 2:32 AM, Ben Horgan wrote:
>>> On 1/14/26 19:09, Reinette Chatre wrote:
>>>> On 1/13/26 6:49 AM, Ben Horgan wrote:
>>>>> The commit 3b497c3f4f04 ("fs/resctrl: Introduce the interface to display
>>>>> monitoring modes") introduced CONFIG_RESCTRL_ASSIGN_FIXED but did not add
>>>>> the kconfig entry. Add this.
>>>>>
>>>>> Also, take the opportunity ensure that any user attempt to change the
>>>>> assign mode fails from the resctrl code rather than delegating to the arch
>>>>> specific code and let the user know by adding a message in last_cmd_status.
>>>>
>>>> Why *any* attempt? Avoiding delegating to arch seems ok as a goal but this change
>>>> additionally changes interface with user space. Current behavior when user writes
>>>> existing mode to the file is to just return success. For example, if current mode
>>>> is "default" and user writes "default". This patch changes this behavior to fail
>>>> instead. Is this intended?
>>>
>>> Intended but as you point out, it would be best to accept the current
>>> value without error for maximum compatibility between architectures.
>>> I'll update the config option help text to reflect this. Was the help
>>> text also discussed previously?
>>
>> It is not clear to me which help text you are referring to. Could you
>> please point me to it?
> 
> I just mean the description in Kconfig. Maybe I'm using the wrong
> terminology?

Counter assignment mode is the right terminology and used throughout the resctrl
documentation.

> 
> From this patch:
>     help
>      Enabled by the architecture when the counter assignment mode is not
>      configurable. This ensures that counter assignment is not

nit: I recommend above "counter assignment" be "counter assignment mode" to be specific
that this is about the *mode* being configurable and not talking about the actual counter
assignment.

Also please ensure that the formatting adheres to the guidance in "Kconfig configuration
files" in Documentation/process/coding-style.rst. Specifically, "help text is indented an
additional two spaces".

> advertised as
>      configurable and configuration attempts fail.

"configuration attempts" -> "attempts to change counter assignment mode"?

As a sidenote, if I understand correctly, MPAM can actually support changing the mode
when it is in "free running" mode (when there are enough counters/monitors available). It
seems to me these systems *could* advertise something like:

	# cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
	[default]
	mbm_event

It is not clear to me if there is a scenario that would benefit from such capability though.
I just bring this up to confirm whether CONFIG_RESCTRL_ASSIGN_FIXED is something that
MPAM enabling wants to enforce for all platforms?

Reinette