On Tue, Aug 26, 2025 at 04:53:51PM +0100, Robin Murphy wrote: [...] > > Genearlly, AUX events generate interrupts based on AUX ring buffer > > watermark but not the period. Seems to me, it is correct to set the > > PERF_PMU_CAP_SAMPLING flag for them. > > This cap is given to drivers which handle event->attr.sample_period and call > perf_event_overflow() - or in a few rare cases, perf_output_sample() > directly - to do something meaningful with it, since the intent is to convey > "I properly handle events for which is_sampling_event() is true". My > understanding is that aux events are something else entirely, but I'm happy > to be corrected. If the discussion is based only on this patch, my understanding is that the PERF_PMU_CAP_SAMPLING flag replaces the PERF_PMU_CAP_NO_INTERRUPT flag for checking whether a PMU event needs to be re-enabled in perf_adjust_freq_unthr_context(). AUX events can trigger a large number of interrupts under certain conditions (e.g., if we set a very small watermark). This is why I conclude that we need to set the PERF_PMU_CAP_SAMPLING flag to ensure that AUX events are re-enabled properly after throttling (see perf_adjust_freq_unthr_events()). > Otherwise, perhaps this suggests it deserves to be named a little more > specifically for clarity, maybe PERF_CAP_SAMPLING_EVENTS? Seems to me, the naming is not critical. If without setting the PERF_PMU_CAP_SAMPLING flag, AUX events might lose chance to be re-enabled after throttling. Thanks, Leo
