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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. Thanks, Ravi