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Since the sample period is programmed in these control registers, >>>> IBS PMU driver allows opening an IBS event by setting sample period >>>> value directly in perf_event_attr->config instead of using explicit >>>> perf_event_attr->sample_period interface. >>>> >>>> However, this logic is not applicable for freq mode events since the >>>> semantics of control register fields are applicable only to fixed >>>> sample period whereas the freq mode event adjusts sample period after >>>> each and every sample. Currently, IBS driver (unintentionally) allows >>>> creating freq mode event via ->config interface, which is semantically >>>> wrong as well as detrimental because it can be misused to bypass >>>> perf_event_max_sample_rate checks. >>> >>> Then let's fix those rate checks? >>> >>> AFAICS this patch limits functionality because the IBS driver would >>> have to be fixed/enhanced to support frequency based events? >>> >>> I'd strongly favor fixing/enhancing the driver instead, as 'perf top -F >>> 1000' is easy to use and it is a useful concept. >> >> No. This patch does not prevent opening an IBS event in freq mode. User >> can still open freq mode IBS event with usual interface attr->freq=1 and >> attr->sample_freq=. i.e. 'perf top -F 1000' with IBS event will >> work fine with this patch. > > Oh, I see - the regular tooling uses perf_event_attr->sample_period, right? Correct. > Never mind then. No worries. Thanks for the review :) Thanks, Ravi