Re: [RFC] mpam,x86,fs/resctrl: Generic schema description Proof of Concept

[Chen, Yu C]

Hi Reinette,

On 6/3/2026 11:45 AM, Reinette Chatre wrote:
> Hi Chenyu,

[ ... ]

> > Thanks for re-spinning this patch set.
> > Looking at commit (fs/resctrl: Introduce additional schema properties),
> > the newly added properties appear to be implemented for the
> > MBA resctrl_membw controller.
>
> Please do note that the "struct resctrl_membw" naming is temporary. I only kept
> current naming to help folks find where existing known structures land in this new
> design but the "struct resctrl_membw" name is not appropriate moving forward.
>
> When user space interacts with the new controls the intention is that each control
> has a "type" that the user can find in the new "type" file and depending on that value
> the user will know what other files/properties can be expected.
>
> In this PoC there are two types: "scalar" and "bitmap" and each is associated with
> a struct that contains the properties associated with that type.
>
> Considering this, these structures could, for example, be renamed as (very long):
> struct resctrl_membw -> struct resctrl_ctrl_scalar
> struct resctrl_cache -> struct resctrl_ctrl_bitmap

OK, the type field serves as the primary key for querying other properties.
Alongside the "type" entry, there also exists a "flag" property. I haven't
spotted this field within resctrl_membw, though it appears in resctrl_cache
via arch_has_sparse_bitmasks. Would it make sense to introduce a dedicated
enum for this flag, or alternatively reuse the existing bw_delay_linear 
for MBA?

> > Would it make sense for these properties to be generic across all resctrl
> > controllers, CAT included? Should they consequently be relocated into
> > struct resctrl_ctrl if that approach is appropriate?
>
> If there are properties that are common across all controls of all types
> then they should be moved to struct resctrl_ctrl. Current examples are "type"
> and "scope" that user space can expect from every control. It is not obvious to
> me at this time what other properties we can designate as common in this way.
>
> For bitmaps there is already the properties that are available in the top-level
> directory. These can just be replicated as properties into the resource_schemata,
> but perhaps using new names as suggested by Dave in
> https://lore.kernel.org/lkml/aQOUAeVP9oc7RIn%2F@xxxxxxxxxxxxxxx/

Got it. Will further look into the code.

thanks,
Chenyu