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

[Babu Moger <bmoger@amd.com>]

Hi Everyone,

On 11/10/25 20:44, Aaron Tomlin wrote:
> On Tue, Nov 11, 2025 at 01:40:45AM +0000, 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
>>
>> Rather than Aaron's
>>
>> 	# echo "L3:*=0" > schemata
> Hi Tony,
>
> I am satisfied with either approach.
>
> However, to clarify, the primary function of the "io_alloc_min_cbm_all"
> interface is to efficiently set the lowest architecturally valid CBM across
> all shared L3 domains. This operation relies entirely on
> r->cache.min_cbm_bits. Since this value is guaranteed by the hardware to be
> valid, this approach is robust and will not return an error (e.g., -EINVAL)
> to userspace.
>
>

Here’s my understanding of the discussion from this thread:


We plan to support the following operation:

    #echo "*=value" > /sys/fs/resctrl/info/L3/io_alloc_cbm


Its users responsibility to make sure the value is valid based on

/sys/fs/resctrl/info/L3/min_cbm_bits and /sys/fs/resctrl/info/L3/cbm_mask.


There’s no need for an additional interface like
|/sys/fs/resctrl/info/L3/io_alloc_min_cbm_all|.


Did I miss anything?


Thanks
Babu