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These are named "mon_sub_L3_YY" >> where "YY" is the node number. >> >> + When supported the mbm_cntr_assign mode allows users to assign a > > "When supported" -> "When enabled"? Or perhaps just drop that and start with > "mbm_cntr_assign mode allows users ..." ok. > > >> + counter to mon_hw_id, event pair enabling bandwidth monitoring for >> + as long as the counter remains assigned. The hardware will continue >> + tracking the assigned mon_hw_id until the user manually unassigns >> + it, ensuring that counters are not reset during this period. With >> + a limited number of counters, the system may run out of assignable >> + counters. In that case, MBM event counters will return 'Unassigned' >> + when the event is read. Users must manually assign a counter to read >> + the events. >> + >> "mon_hw_id": >> Available only with debug option. The identifier used by hardware >> for the monitor group. On x86 this is the RMID. >> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c >> index 200d89a64027..8e265a86e524 100644 >> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c >> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c >> @@ -527,6 +527,12 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r, >> /* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */ >> lockdep_assert_cpus_held(); >> >> + if (resctrl_arch_mbm_cntr_assign_enabled(r) && is_mbm_event(evtid) && >> + !mbm_cntr_assigned(r, d, rdtgrp, evtid)) { >> + rr->err = -ENOENT; >> + return; >> + } >> + > > hmmm ... d can be NULL here after the SNC support. Since the file that needs a > sum is essentially software backed I do not think assigning counters would > apply to it (but it may theoretically apply to the domains it consists of). > I think it may be safer to just move this check into rdtgroup_mondata_show() > where it reads data for a single domain. Sure. > > I am not sure if we need to change the documentation because of this. One option > could be a rewording to "MBM event counters may return 'Unassigned' or > 'Unavailable' when the event is read". ok. Thanks Babu