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Reading QM_CTR will then return the contents of the specified >>>> counter ID. The E bit will be set if the counter configuration was invalid, >>> >>> Where is "the E bit" defined? >> >> QM_CTR MSRS bits >> >> Bits Mnemonic Description. >> 63 E Error on access to counter >> 62 U Count for this event is currently unavailable >> 61-CNT_LEN _ Reserved, read as zero >> CNT_LEN-1:0 CNT Count of monitored resource or event >> >> >> The bit 63 is "E bit" -> RMID_VAL_ERROR >> the bit 62 is "U bit" -> RMID_VAL_UNAVAIL >> >> How about? >> >> The RMID_VAL_ERROR bit will be set if the counter configuration >> was invalid, or if an invalid counter ID was set in the QM_EVTSEL[RMID] field > > It is not clear to me why the comments only mention one of the error bits handled > in the code. > The motivation for hardware counters is that reading of RMID may return > "Unavailable". Does this imply that reading a hardware counter should > never return "Unavailable"? Why is this error handled as possible when > reading a counter though? Checked again here. Yes. RMID_VAL_UNAVAIL is also a possibility. I should have added the text before. > > >>>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c >>>> index a230d98e9d73..026c2e2d19d3 100644 >>>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c >>>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c >>>> @@ -259,6 +259,76 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_mon_domain *d, >>>> return 0; >>>> } >>>> >>>> +static int __cntr_id_read(u32 cntr_id, u64 *val) >>>> +{ >>>> + u64 msr_val; >>>> + >>>> + /* >>>> + * QM_EVTSEL Register definition: >>>> + * ======================================================= >>>> + * Bits Mnemonic Description >>>> + * ======================================================= >>>> + * 63:44 -- Reserved >>>> + * 43:32 RMID Resource Monitoring Identifier >>>> + * 31 ExtEvtID Extended Event Identifier >>>> + * 30:8 -- Reserved >>>> + * 7:0 EvtID Event Identifier >>>> + * ======================================================= >>>> + * The contents of a specific counter can be read by setting the >>>> + * following fields in QM_EVTSEL.ExtendedEvtID(=1) and >>>> + * QM_EVTSEL.EvtID = L3CacheABMC (=1) and setting [RMID] to the >>>> + * desired counter ID. Reading QM_CTR will then return the >>>> + * contents of the specified counter. The E bit will be set if the >>>> + * counter configuration was invalid, or if an invalid counter ID >>>> + * was set in the QM_EVTSEL[RMID] field. >>> >>> (same comments as changelog) >> >> "The E bit" -> "The RMID_VAL_ERROR bit" > > For comments to be accurate, per the handling that follows, RMID_VAL_UNAVAIL > is also a possibility, or is it not actually possible and just coded to match > RMID reading? > Added the text now. "The RMID_VAL_UNAVAIL bit will be set if the counter data is not currently available." -- Thanks Babu Moger