Re: [PATCH v4] fs/resctrl: Add CONFIG_RESCTRL_ASSIGN_FIXED Kconfig entry

[Reinette Chatre]

Hi Ben,

On 3/2/26 2:02 AM, Ben Horgan wrote:
> Hi Boris,
> 
> On 3/1/26 10:49, Borislav Petkov wrote:
>> On Wed, Feb 04, 2026 at 04:19:52PM +0000, Ben Horgan wrote:
>>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>>> index 572a9925bd6c..4e9f55ee3267 100644
>>> --- a/fs/resctrl/monitor.c
>>> +++ b/fs/resctrl/monitor.c
>>> @@ -1451,6 +1451,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
>>>  	}
>>>  
>>>  	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>>> +		if (IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
>>
>> Does it need to be a Kconfig entry or you can figure out programatically from
>> the architecture that that is the case and avoid yet another CONFIG_ knob?
>>
>> From reading this, I'm thinking
>>
>> 		if (IS ARM64) {
>>
>> should do or...?
> 
> Yes, we don't necessarily need the Kconfig and we don't necessarily need this condition at all in
> resctrl_mbm_assign_mode_write(), we do need the existing one in resctrl_mbm_assign_mode_show() though.

It is not obvious to me why the one in resctrl_mbm_assign_mode_show() is required if
a new arch helper could suffice in other parts 

> 
> The Kconfig was effectively added in:
> 
> commit 3b497c3f4f04 ("fs/resctrl: Introduce the interface to display monitoring modes")
> 
> and I was just filling in the missing piece. Most arch specific things in resctrl seem
> to be dealt with using resctrl_arch_* hooks. Would it be preferable to create a new one of these?

It looks to me as though this patch fits in with the other series you posted at
https://lore.kernel.org/lkml/20260225201905.3568624-1-ben.horgan@xxxxxxx/

When looking at this patch together with the other series there may indeed be an arch
helper that can replace CONFIG_RESCTRL_ASSIGN_FIXED but as I mentioned in that series
the MPAM capabilities and strategies for resctrl to support them are not clear to me
at this time.


> It could be resctrl_arch_mbm_cntr_assign_fixed() although we seem to be getting too many
> of these too. Perhaps we could extend the meaning of another hook, resctrl_arch_mbm_assign_set() could

Could you please elaborate which category of helper is getting to be too many? We can surely
explore improvements.

> return -EOPNOTSUPP to indicate to resctrl that the counter assignment mode is not configurable.
> 

Reinette