Re: [PATCH v2 4/6] fs/resctrl: Disallow the software controller when mbm counters are assignable

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

Hi Ben,

On 3/13/26 10:45 AM, Ben Horgan wrote:
> The software controller requires that there are free running mbm counters

How is "free running" defined?

(sidenote: please use upper case for acronyms throughout: mbm -> MBM)

> for each control group in order to provide the feedback necessary to
> control the memory bandwidth allocation for that control group.  Previous
> to the introduction counter assignment support (ABMC) resctrl required this

I am not able to parse this second sentence. "to the introduction" -> "to
the introduction of"? What does "this" refer to?

> in order to advertise support for mbm but now if the mbm counters are
> assignable then this can't be guaranteed.
> 
> Currently, only AMD systems support counter assignment but the MBA is non
> linear and so the software controller is never supported anyway. For MPAM
> systems the MBA is linear and so the dependency on counters not being
> assignable needs to made explicit. Hence, fail the mount if the user

It is not clear to me that software controller depends on counters not being
assignable. Is the problem not instead that the current implementation does not
support this since it allows the event used by software controller to not have a
counter assigned? So, instead of adding support for software controller by ensuring
that the event used by software controller has a counter assigned, this patch opts
for the simpler disabling of software controller when assignable counters are in use?

> requests the software controller, the mba_MBps option, and the mbm counters
> are assignable.

Reinette