Re: [PATCH 1/2] x86/resctrl: Add io_alloc_min_cbm_all interface for CBM reset

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Tony,

On 11/10/25 5:40 PM, Luck, Tony wrote:
>> Seems like user space has needed information to perform a sane reset?
> 
> Like this:
> 
> 1) 	Read info files to figure out what minimum mask is needed for this system
> 2)	Use Babu's suggested syntax of
> 		# echo "L3:*={min_mask_from_step_1}" > schemata

Exactly, but without the "L3:" and with s/schemata/io_alloc_cbm/. Specifically,
	# echo "*={min_mask_from_step_1}" > /sys/fs/resctrl/info/L3/io_alloc_cbm

I do not believe this feature is being considered for the schemata file (at this time?),
just for io_alloc_cbm.

> 
> Rather than Aaron's
> 
> 	# echo "L3:*=0" > schemata
> 
> I'm OK with this for L3, but still see it being less useful for L2 with asymmetric domains.

That would first require that these L2 with asymmetric domains be made available
as resource for IO allocation. At this time the feature is limited to L3 but when/if it
expands to L2 an interface like this could remain sane by allowing values that overlap all
domains to be set on all domains with one user space call and a clear failure presented
to user via last_cmd_status on first failure if it is not possible. 

> 
> It can meet the "set a minimum value across all domains" need.

ack.

> 
> But can fail setting a value that isn't supported by some of the domains.
> 

ack.

Reinette