Re: [RFC PATCH 01/19] x86,fs/resctrl: Add support for Global Bandwidth Enforcement (GLBE)

[Reinette Chatre]

Hi Ben,

On 2/20/26 2:07 AM, Ben Horgan wrote:
> 
> I haven't fully understood what GLBE is but in MPAM we have an optional
> feature in MSC (MPAM devices) called partid narrowing. For some MSC
> there are limited controls and the incoming partid is mapped to an
> effective partid using a mapping. This mapping is software controllable.
> Dave (with Shaopeng and Zeng) has a proposal to use this to use partid
> bits as pmg bits, [1]. This usage would have to be opt-in as it changes
> the number of closid/rmid that MPAM presents to resctrl. If however, the
> user doesn't use that scheme then the controls could be presented as
> controls for groups of closid in resctrl. Is this similar/usable with
> the same interface as GLBE or have I misunderstood?
> 
> [1]
> https://lore.kernel.org/linux-arm-kernel/20241212154000.330467-1-Dave.Martin@xxxxxxx/

On a high level these look like different capabilities to me but I look forward to
hear from others to understand where I may be wrong.

As I understand the feature you refer to is a way in which MPAM can increase the
number of hardware monitoring IDs available(*). It does so by using the PARTID
narrowing feature while taking advantage of the fact that PARTID for filtering
resource monitors is always a "request PARTID". In itself I understand the PARTID
narrowing feature to manage how resource allocation of a *single* "MPAM component"
is managed.

On the other hand I see GLBE as a feature that essentially allows the scope of
allocation to span multiple domains/components.

As I see it, applying GLBE to MPAM would need the capability to, for example,
set a memory bandwidth MAX that is shared across multiple MPAM components.

Reinette

* as a sidenote it is not clear to me why this would require an opt-in since
  there only seems benefits to this.