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

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