Hi Peter, On 5/21/25 7:27 AM, Peter Newman wrote: > On Wed, May 21, 2025 at 1:44 AM Reinette Chatre > <reinette.chatre@xxxxxxxxx> wrote: >> On 5/20/25 4:25 PM, Moger, Babu wrote: ... >>> >>> Here’s my current understanding of soft-ABMC. Peter may have a more in-depth perspective on this. >>> >>> Soft-ABMC: >>> a. num_mbm_cntrs: This is a software-defined limit based on the number of active RMIDs that can be supported. The value can be obtained using the code referenced in [4]. >>> >>> b. Assignments: No hardware configuration is required. We simply need to ensure that no more than num_mbm_cntrs RMIDs are active at any given time. >>> >>> c. Configuration: Controlled via /info/L3_MON/mbm_total_bytes_config and mbm_local_bytes_config. >>> >>> d. Events: Only two events can be assigned(local and total). >>> >>> ABMC: >>> a. num_mbm_cntrs: This is defined by the hardware. >>> b. Assignments: Requires special MSR writes to assign counters. >>> c. Configuration: Comes from /info/L3_MON/counter_configs/. >>> d. Events: More than two events can be assigned to a group (currently up to 2). >>> >>> Commonalities: >>> a. Assignments can be either exclusive or shared in both these modes. >>> >>> Given these, I believe we can easily accommodate soft-ABMC in this interface. >> >> This is not so obvious to me. It looks to me as though the user is forced to interpret >> the content of resctrl files differently based on soft-ABMC vs ABMC making the interface >> inconsistent and user thus needing to know details of implementations. This is what the previous >> discussion I linked to aimed to address. It sounds to me as though you believe that this is no longer >> an issue. Could you please show examples of what a user can expect from the interfaces and how a user >> will interact with the interfaces on both a non-ABMC and ABMC system? > > At the interface level, I think mbm_L3_assignments on a non-ABMC > system would only need to contain a single line: > > 0=s;1=s;...;31=s It should be obvious to user space how to interpret the fields. When there is thus a single "mbm_cntr_assign" mode used for ABMC and soft-ABMC a single line like this would be difficult to parse since that would imply/require that user space knows whether it is running on ABMC or soft-ABMC system, which we should avoid. If there are different modes, for example "mbm_cntr_event_assign" and "mbm_cntr_group_assign" then this could be used by user space to distinguish how to interact with mbm_L3_assignments making something like this possible. > > But maybe for consistency we would synthesize a single, unmodifiable > counter configuration to reflect that allocating an RMID in a domain > results in assignment to all events and deallocating the RMID > unassigns all events. We could call it "group" to say it's assigning > at the group level, or perhaps just '*': > > *:0=s;1=s;...;31=s > > I'm not sure about allowing a '*' on ABMC hardware, because it could > be interpreted as allocating a lot of counters when a large number of > event configurations exist. > > *:0=s;1=s;...;31=s > Either could work also. Whether it is "group" or "*" ABMC systems could respond with "not supported". Will think about this more but would like to hear your opinion about the flexibility that distinguishing between a "mbm_cntr_event_assign" and "mbm_cntr_group_assign" mode provides. Reinette > -Peter > > >> >> Thank you >> >> Reinette >> >>> >>>>>> >>>>>> [2] https://lore.kernel.org/lkml/afb99efe-0de2-f7ad-d0b8-f2a0ea998efd@xxxxxxx/ >>>>>> [3] https://lore.kernel.org/lkml/CALPaoCg3KpF94g2MEmfP_Ro2mQZYFA8sKVkmb+7isotKNgdY9A@xxxxxxxxxxxxxx/ >>>>> >>>> >>>> >>> >>
