1 // SPDX-License-Identifier: GPL-2.0-only
3  * menu.c - the menu idle governor
5  * Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
33  * state:
39  * -----------------------
40  * C state entry and exit have an energy cost, and a certain amount of time in
41  * the  C state is required to actually break even on this cost. CPUIDLE
43  * need is a good prediction of how long we'll be idle. Like the traditional
56  * expect 500 milliseconds of idle time the likelihood of getting an interrupt
57  * very early is much higher than if we expect 50 micro seconds of idle time.
61  * Repeatable-interval-detector
62  * ----------------------------
110 	s64 value, min_thresh = -1, max_thresh = UINT_MAX;  in get_typical_interval()
123 		value = data->intervals[i];  in get_typical_interval()
155 	variance -= avg_sq;  in get_typical_interval()
199 	if (avg - min > max - avg)  in get_typical_interval()
208  * menu_select - selects the next idle state to enter
209  * @drv: cpuidle driver containing state data
217 	s64 latency_req = cpuidle_governor_latency_req(dev->cpu);  in menu_select()
222 	if (data->needs_update) {  in menu_select()
224 		data->needs_update = 0;  in menu_select()
227 	/* Find the shortest expected idle interval. */  in menu_select()
239 		data->next_timer_ns = delta;  in menu_select()
240 		data->bucket = which_bucket(data->next_timer_ns);  in menu_select()
244 					data->next_timer_ns *  in menu_select()
245 						data->correction_factor[data->bucket],  in menu_select()
247 		/* Use the lowest expected idle interval to pick the idle state. */  in menu_select()
256 		data->next_timer_ns = KTIME_MAX;  in menu_select()
258 		data->bucket = BUCKETS - 1;  in menu_select()
261 	if (unlikely(drv->state_count <= 1 || latency_req == 0) ||  in menu_select()
262 	    ((data->next_timer_ns < drv->states[1].target_residency_ns ||  in menu_select()
263 	      latency_req < drv->states[1].exit_latency_ns) &&  in menu_select()
264 	     !dev->states_usage[0].disable)) {  in menu_select()
266 		 * In this case state[0] will be used no matter what, so return  in menu_select()
267 		 * it right away and keep the tick running if state[0] is a  in menu_select()
270 		*stop_tick = !(drv->states[0].flags & CPUIDLE_FLAG_POLLING);  in menu_select()
277 		 * idle duration misprediction is much higher, because the CPU  in menu_select()
278 		 * may be stuck in a shallow idle state for a long time as a  in menu_select()
280 		 * the known time till the closest timer event for the idle  in menu_select()
281 		 * state selection.  in menu_select()
284 			predicted_ns = data->next_timer_ns;  in menu_select()
290 	 * Find the idle state with the lowest power while satisfying  in menu_select()
293 	idx = -1;  in menu_select()
294 	for (i = 0; i < drv->state_count; i++) {  in menu_select()
295 		struct cpuidle_state *s = &drv->states[i];  in menu_select()
297 		if (dev->states_usage[i].disable)  in menu_select()
300 		if (idx == -1)  in menu_select()
301 			idx = i; /* first enabled state */  in menu_select()
303 		if (s->target_residency_ns > predicted_ns) {  in menu_select()
305 			 * Use a physical idle state, not busy polling, unless  in menu_select()
308 			if ((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) &&  in menu_select()
309 			    s->exit_latency_ns <= latency_req &&  in menu_select()
310 			    s->target_residency_ns <= data->next_timer_ns) {  in menu_select()
311 				predicted_ns = s->target_residency_ns;  in menu_select()
320 				 * If the state selected so far is shallow,  in menu_select()
325 				predicted_ns = drv->states[idx].target_residency_ns;  in menu_select()
330 			 * If the state selected so far is shallow and this  in menu_select()
331 			 * state's target residency matches the time till the  in menu_select()
335 			if (drv->states[idx].target_residency_ns < TICK_NSEC &&  in menu_select()
336 			    s->target_residency_ns <= delta_tick)  in menu_select()
341 		if (s->exit_latency_ns > latency_req)  in menu_select()
347 	if (idx == -1)  in menu_select()
351 	 * Don't stop the tick if the selected state is a polling one or if the  in menu_select()
352 	 * expected idle duration is shorter than the tick period length.  in menu_select()
354 	if (((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||  in menu_select()
358 		if (idx > 0 && drv->states[idx].target_residency_ns > delta_tick) {  in menu_select()
361 			 * residency of the state to be returned is not within  in menu_select()
365 			for (i = idx - 1; i >= 0; i--) {  in menu_select()
366 				if (dev->states_usage[i].disable)  in menu_select()
370 				if (drv->states[i].target_residency_ns <= delta_tick)  in menu_select()
380  * menu_reflect - records that data structures need update
382  * @index: the index of actual entered state
391 	dev->last_state_idx = index;  in menu_reflect()
392 	data->needs_update = 1;  in menu_reflect()
393 	data->tick_wakeup = tick_nohz_idle_got_tick();  in menu_reflect()
397  * menu_update - attempts to guess what happened after entry
398  * @drv: cpuidle driver containing state data
404 	int last_idx = dev->last_state_idx;  in menu_update()
405 	struct cpuidle_state *target = &drv->states[last_idx];  in menu_update()
411 	 * power state and occurrence of the wakeup event.  in menu_update()
413 	 * If the entered idle state didn't support residency measurements,  in menu_update()
421 	 * assume the state was never reached and the exit latency is 0.  in menu_update()
424 	if (data->tick_wakeup && data->next_timer_ns > TICK_NSEC) {  in menu_update()
427 		 * the tick boundary (if the tick was stopped), but the idle  in menu_update()
431 		 * have been idle long (but not forever) to help the idle  in menu_update()
435 	} else if ((drv->states[last_idx].flags & CPUIDLE_FLAG_POLLING) &&  in menu_update()
436 		   dev->poll_time_limit) {  in menu_update()
438 		 * The CPU exited the "polling" state due to a time limit, so  in menu_update()
439 		 * the idle duration prediction leading to the selection of that  in menu_update()
440 		 * state was inaccurate.  If a better prediction had been made,  in menu_update()
441 		 * the CPU might have been woken up from idle by the next timer.  in menu_update()
444 		measured_ns = data->next_timer_ns;  in menu_update()
447 		measured_ns = dev->last_residency_ns;  in menu_update()
450 		if (measured_ns > 2 * target->exit_latency_ns)  in menu_update()
451 			measured_ns -= target->exit_latency_ns;  in menu_update()
457 	if (measured_ns > data->next_timer_ns)  in menu_update()
458 		measured_ns = data->next_timer_ns;  in menu_update()
461 	new_factor = data->correction_factor[data->bucket];  in menu_update()
462 	new_factor -= new_factor / DECAY;  in menu_update()
464 	if (data->next_timer_ns > 0 && measured_ns < MAX_INTERESTING)  in menu_update()
466 					data->next_timer_ns);  in menu_update()
469 		 * we were idle so long that we count it as a perfect  in menu_update()
483 	data->correction_factor[data->bucket] = new_factor;  in menu_update()
485 	/* update the repeating-pattern data */  in menu_update()
486 	data->intervals[data->interval_ptr++] = ktime_to_us(measured_ns);  in menu_update()
487 	if (data->interval_ptr >= INTERVALS)  in menu_update()
488 		data->interval_ptr = 0;  in menu_update()
492  * menu_enable_device - scans a CPU's states and does setup
499 	struct menu_device *data = &per_cpu(menu_devices, dev->cpu);  in menu_enable_device()
509 		data->correction_factor[i] = RESOLUTION * DECAY;  in menu_enable_device()
523  * init_menu - initializes the governor