Re: [PATCH v6 2/3]: perf/core: use context tstamp_data for skipped events on mux interrupt

[Alexey Budankov]

On 04.08.2017 15:51, Peter Zijlstra wrote:
> On Fri, Aug 04, 2017 at 02:35:34PM +0200, Peter Zijlstra wrote:
>> Something like:
>>
>> __update_state_and_time(event, new_state)
>> {
>> 	u64 delta, now = perf_event_time(event);
>> 	int old_state = event->state;
>>
>> 	event->tstamp = now;
>> 	event->state  = new_state;
>>
>> 	delta = now - event->tstamp;
> Obv should go above the tstamp assignment
> 
>> 	switch (state) {
>> 	case STATE_ACTIVE:
>> 		WARN_ON_ONCE(old_state != STATE_INACTIVE);
>> 		event->total_time_enabled += delta;
>> 		break;
>>
>> 	case STATE_INACTIVE:
>> 		switch (old_state) {
>> 		case STATE_OFF:
>> 			/* ignore the OFF -> INACTIVE period */
>> 			break;
>>
>> 		case STATE_ACTIVE:
>> 			event->total_time_enabled += delta;
>> 			event->total_time_running += delta;
>> 			break;
>>
>> 		default:
>> 			WARN_ONCE();
>> 		}
>> 		break;
>>
>> 	case STATE_OFF:
>> 		WARN_ON_ONCE(old_state != STATE_INACTIVE)
>> 		event->total_time_enabled += delta;
>> 		break;
>> 	}
>> }
> 
> So that's a straight fwd state machine that deals with:
> 
>   OFF <-> INACTIVE <-> ACTIVE
> 
> but I think something like:
> 
> __update_state_and_time(event, new_state)
> {
> 	u64 delta, new = perf_event_time(event);
> 	int old_state = event->state;
> 
> 	delta = now - event->tstamp;
> 	event->tstamp = now;
> 	event->state  = new_state;
> 
> 	if (old_state == STATE_OFF)
> 		return;
> 
> 	event->total_time_enabled += delta;
> 
> 	if (old_state == STATE_ACTIVE)
> 		event->total_time_running += delta;
> }
> 
> is equivalent and generates smaller code.. but again, double check (also
> it doesn't validate the state transitions).

Accepted.

>