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The ability to go back to legacy was added while looking ahead to support the next "assignable counter" feature that is software based ("soft-RMID" .. "soft-ABMC"?). This series adds support for ABMC on recent AMD hardware to address the issue described in cover letter. This issue also exists on earlier AMD hardware that does not have the ABMC feature and Peter is working on a software solution to address the issue on non-ABMC hardware. This software solution is expected to have the same interface as the hardware solution but earlier discussions revealed that it may introduce extra latency that users may only want to accept during periods of active monitoring. Thus the option to disable the counter assignment mode. Your point about users returning to "legacy" mode on ABMC hardware is valid. I do not know if that is useful. Here I can only speculate since monitoring with ABMC is more accurate but also requires more user space involvement to assign counters while legacy mode is less accurate while requiring less user space involvement. > For MPAM I'm looking at enabling this on any platform that is short of monitors. If > user-space disables it I don't have a "at random" hardware behaviour to fall back on - its > extra work to invent a behaviour I'm not sure is useful... It should not be required for MPAM to have a "legacy" mode. resctrl fs can expose only one mode that is always enabled. Noting this now is important so that we can get the wording right in the documentation. Thanks for chiming in on MPAM's plans for this work. Reinette