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The current status >>>>>        quo for x86. >>>>>     - global_assign_ctrl_inherit_mon >>>>>        When active, CLOSID/control group can be assigned for *all* (hence, "global") >>>>>        kernel work while all kernel work uses same RMID as user space. >>>>>        Can only be supported on architecture where CLOSID and RMID are independent. >>>>>        An arch may support this in hardware (RMID_EN=0?) or this can be done by resctrl during >>>>>        context switch if the RMID is independent and the context switches cost is >>>>>        considered "reasonable". >>>>>        This supports use case https://lore.kernel.org/lkml/CABPqkBSq=cgn-am4qorA_VN0vsbpbfDePSi7gubicpROB1=djw@mail.gmail.com/ >>>>>        for PLZA. >>>>>     - global_assign_ctrl_assign_mon >>>>>        When active the same resource group (CLOSID and RMID) can be assigned to >>>>>        *all* kernel work. This could be any group, including the default group. >>>>>        There may not be a use case for this but it could be useful as an intemediate >>>>>        step of the mode that follow (more later). >>>>>     - per_group_assign_ctrl_assign_mon >>>>>        When active every resource group can be associated with another (or the same) >>>>>        resource group. This association maps the resource group for user space work >>>>>        to resource group for kernel work. This is similar to the "kernel_group" idea >>>>>        presented in: >>>>>        https://lore.kernel.org/lkml/aYyxAPdTFejzsE42@e134344.arm.com/ >>>>>        This addresses use case https://lore.kernel.org/lkml/CABPqkBSq=cgn-am4qorA_VN0vsbpbfDePSi7gubicpROB1=djw@mail.gmail.com/ >>>>>        for MPAM. >>>> All these new names and related information will go in global structure. >>>> >>>> Something like this.. >>>> >>>> Struct kern_mode { >>>>         enum assoc_mode; >>>>         struct rdtgroup *k_rdtgrp; >>>>         ... >>>> }; >>>> >>>> Not sure what other information will be required here. Will know once I stared working on it. >>>> >>>> This structure will be updated based on user echo's in "kernel_mode" and "kernel_mode_assignment". >>> This looks to be a good start. I think keeping the rdtgroup association is good since >>> it helps to easily display the name to user space while also providing access to the CLOSID >>> and RMID that is assigned to the tasks. >>> By placing them in their own structure instead of just globals it does make it easier to >>> build on when some modes have different requirements wrt rdtgroup management. >> I am not clear on this comment. Can you please elaborate little bit? > I believe what you propose should suffice for the initial support for PLZA. I do not > see the PLZA enabling needing anything more complicated. > > As I understand for MPAM support there needs to be more state to track which privilege level > tasks run at. > > So, when just considering how MPAM may build on this: The PARTID/PMG to run at when in kernel mode > can be managed per group or per task. In either case I suspect that struct task_struct would need > to include the kernel mode PARTID/PMG to support setting the correct kernel mode PARTID/PMG during > context switching similar to what you coded up in this initial RFC. MPAM may choose to have struct > task_struct be the only place to keep all state about which PARTID/PMG to run when in kernel mode > but I suspect that may result in a lot of lock contention (user space could, for example, be able > to lock up the entire system with a loop reading info/kernel_mode_assignment) so MPAM may choose to > expand the struct kernel_mode introduced by PLZA to, (if kernel mode is managed per group) instead > of one struct rdtgroup * contain a mapping of every resource group to the resource group that should > be used for kernel mode work. This could be some staging/cache used between user space and all the > task structures to help manage the state. > > I do not know what MPAM implementation may choose to do but as I see it your proposal > provides a good foundation to build on since it establishes a global place, struct kernel_mode, > where all such state can/should be stored instead of some unspecified group of global variables. > Sounds good. Thanks for the clarification. Thanks Babu