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Yes, the duplicate start can happen > Also, if pt_syscore_resume() skips calling pt_event_start() when the event is > throttled, wouldn't clearing pt_suspended_event in pt_syscore_resume() before > perf_event_unthrottle() later calls pt_event_start() cause a throttled > snapshot event to read reset PT MSRs in pt_read_offset() and take the > pt_config_enable() path without reprogramming the output MSRs? Right, so keep the restart and make the redundant start a no-op instead. An event with both PERF_HES_UPTODATE and PERF_HES_STOPPED clear is already running. if (!(hwc->state & PERF_HES_UPTODATE)) { + /* Already running, e.g. restarted by pt_syscore_resume() */ + if (!(hwc->state & PERF_HES_STOPPED)) + return; hwc->state &= ~PERF_HES_STOPPED; One side effect remains. A throttled PT event restarted on resume traces until the next tick while its sibling is still throttled. That lasts at most one tick and is harmless.