Merge back earlier cpuidle material for v5.1.

3 files changed, 455 insertions, 1 deletions

diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index 7e48eb5bf0a7..8caccbbd7353 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -4,7 +4,7 @@ config CPU_IDLE
 	bool "CPU idle PM support"
 	default y if ACPI || PPC_PSERIES
 	select CPU_IDLE_GOV_LADDER if (!NO_HZ && !NO_HZ_IDLE)
-	select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE)
+	select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE) && !CPU_IDLE_GOV_TEO
 	help
 	  CPU idle is a generic framework for supporting software-controlled
 	  idle processor power management.  It includes modular cross-platform
@@ -23,6 +23,15 @@ config CPU_IDLE_GOV_LADDER
 config CPU_IDLE_GOV_MENU
 	bool "Menu governor (for tickless system)"
 
+config CPU_IDLE_GOV_TEO
+	bool "Timer events oriented (TEO) governor (for tickless systems)"
+	help
+	  This governor implements a simplified idle state selection method
+	  focused on timer events and does not do any interactivity boosting.
+
+	  Some workloads benefit from using it and it generally should be safe
+	  to use.  Say Y here if you are not happy with the alternatives.
+
 config DT_IDLE_STATES
 	bool
 
diff --git a/drivers/cpuidle/governors/Makefile b/drivers/cpuidle/governors/Makefile
index 1b512722689f..4d8aff5248a8 100644
--- a/drivers/cpuidle/governors/Makefile
+++ b/drivers/cpuidle/governors/Makefile
@@ -4,3 +4,4 @@
 
 obj-$(CONFIG_CPU_IDLE_GOV_LADDER) += ladder.o
 obj-$(CONFIG_CPU_IDLE_GOV_MENU) += menu.o
+obj-$(CONFIG_CPU_IDLE_GOV_TEO) += teo.o
diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
new file mode 100644
index 000000000000..7d05efdbd3c6
--- /dev/null
+++ b/drivers/cpuidle/governors/teo.c
@@ -0,0 +1,444 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Timer events oriented CPU idle governor
+ *
+ * Copyright (C) 2018 Intel Corporation
+ * Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+ *
+ * The idea of this governor is based on the observation that on many systems
+ * timer events are two or more orders of magnitude more frequent than any
+ * other interrupts, so they are likely to be the most significant source of CPU
+ * wakeups from idle states.  Moreover, information about what happened in the
+ * (relatively recent) past can be used to estimate whether or not the deepest
+ * idle state with target residency within the time to the closest timer is
+ * likely to be suitable for the upcoming idle time of the CPU and, if not, then
+ * which of the shallower idle states to choose.
+ *
+ * Of course, non-timer wakeup sources are more important in some use cases and
+ * they can be covered by taking a few most recent idle time intervals of the
+ * CPU into account.  However, even in that case it is not necessary to consider
+ * idle duration values greater than the time till the closest timer, as the
+ * patterns that they may belong to produce average values close enough to
+ * the time till the closest timer (sleep length) anyway.
+ *
+ * Thus this governor estimates whether or not the upcoming idle time of the CPU
+ * is likely to be significantly shorter than the sleep length and selects an
+ * idle state for it in accordance with that, as follows:
+ *
+ * - Find an idle state on the basis of the sleep length and state statistics
+ *   collected over time:
+ *
+ *   o Find the deepest idle state whose target residency is less than or equal
+ *     to the sleep length.
+ *
+ *   o Select it if it matched both the sleep length and the observed idle
+ *     duration in the past more often than it matched the sleep length alone
+ *     (i.e. the observed idle duration was significantly shorter than the sleep
+ *     length matched by it).
+ *
+ *   o Otherwise, select the shallower state with the greatest matched "early"
+ *     wakeups metric.
+ *
+ * - If the majority of the most recent idle duration values are below the
+ *   target residency of the idle state selected so far, use those values to
+ *   compute the new expected idle duration and find an idle state matching it
+ *   (which has to be shallower than the one selected so far).
+ */
+
+#include <linux/cpuidle.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/sched/clock.h>
+#include <linux/tick.h>
+
+/*
+ * The PULSE value is added to metrics when they grow and the DECAY_SHIFT value
+ * is used for decreasing metrics on a regular basis.
+ */
+#define PULSE		1024
+#define DECAY_SHIFT	3
+
+/*
+ * Number of the most recent idle duration values to take into consideration for
+ * the detection of wakeup patterns.
+ */
+#define INTERVALS	8
+
+/**
+ * struct teo_idle_state - Idle state data used by the TEO cpuidle governor.
+ * @early_hits: "Early" CPU wakeups "matching" this state.
+ * @hits: "On time" CPU wakeups "matching" this state.
+ * @misses: CPU wakeups "missing" this state.
+ *
+ * A CPU wakeup is "matched" by a given idle state if the idle duration measured
+ * after the wakeup is between the target residency of that state and the target
+ * residency of the next one (or if this is the deepest available idle state, it
+ * "matches" a CPU wakeup when the measured idle duration is at least equal to
+ * its target residency).
+ *
+ * Also, from the TEO governor perspective, a CPU wakeup from idle is "early" if
+ * it occurs significantly earlier than the closest expected timer event (that
+ * is, early enough to match an idle state shallower than the one matching the
+ * time till the closest timer event).  Otherwise, the wakeup is "on time", or
+ * it is a "hit".
+ *
+ * A "miss" occurs when the given state doesn't match the wakeup, but it matches
+ * the time till the closest timer event used for idle state selection.
+ */
+struct teo_idle_state {
+	unsigned int early_hits;
+	unsigned int hits;
+	unsigned int misses;
+};
+
+/**
+ * struct teo_cpu - CPU data used by the TEO cpuidle governor.
+ * @time_span_ns: Time between idle state selection and post-wakeup update.
+ * @sleep_length_ns: Time till the closest timer event (at the selection time).
+ * @states: Idle states data corresponding to this CPU.
+ * @last_state: Idle state entered by the CPU last time.
+ * @interval_idx: Index of the most recent saved idle interval.
+ * @intervals: Saved idle duration values.
+ */
+struct teo_cpu {
+	u64 time_span_ns;
+	u64 sleep_length_ns;
+	struct teo_idle_state states[CPUIDLE_STATE_MAX];
+	int last_state;
+	int interval_idx;
+	unsigned int intervals[INTERVALS];
+};
+
+static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
+
+/**
+ * teo_update - Update CPU data after wakeup.
+ * @drv: cpuidle driver containing state data.
+ * @dev: Target CPU.
+ */
+static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
+{
+	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
+	unsigned int sleep_length_us = ktime_to_us(cpu_data->sleep_length_ns);
+	int i, idx_hit = -1, idx_timer = -1;
+	unsigned int measured_us;
+
+	if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) {
+		/*
+		 * One of the safety nets has triggered or this was a timer
+		 * wakeup (or equivalent).
+		 */
+		measured_us = sleep_length_us;
+	} else {
+		unsigned int lat = drv->states[cpu_data->last_state].exit_latency;
+
+		measured_us = ktime_to_us(cpu_data->time_span_ns);
+		/*
+		 * The delay between the wakeup and the first instruction
+		 * executed by the CPU is not likely to be worst-case every
+		 * time, so take 1/2 of the exit latency as a very rough
+		 * approximation of the average of it.
+		 */
+		if (measured_us >= lat)
+			measured_us -= lat / 2;
+		else
+			measured_us /= 2;
+	}
+
+	/*
+	 * Decay the "early hits" metric for all of the states and find the
+	 * states matching the sleep length and the measured idle duration.
+	 */
+	for (i = 0; i < drv->state_count; i++) {
+		unsigned int early_hits = cpu_data->states[i].early_hits;
+
+		cpu_data->states[i].early_hits -= early_hits >> DECAY_SHIFT;
+
+		if (drv->states[i].target_residency <= sleep_length_us) {
+			idx_timer = i;
+			if (drv->states[i].target_residency <= measured_us)
+				idx_hit = i;
+		}
+	}
+
+	/*
+	 * Update the "hits" and "misses" data for the state matching the sleep
+	 * length.  If it matches the measured idle duration too, this is a hit,
+	 * so increase the "hits" metric for it then.  Otherwise, this is a
+	 * miss, so increase the "misses" metric for it.  In the latter case
+	 * also increase the "early hits" metric for the state that actually
+	 * matches the measured idle duration.
+	 */
+	if (idx_timer >= 0) {
+		unsigned int hits = cpu_data->states[idx_timer].hits;
+		unsigned int misses = cpu_data->states[idx_timer].misses;
+
+		hits -= hits >> DECAY_SHIFT;
+		misses -= misses >> DECAY_SHIFT;
+
+		if (idx_timer > idx_hit) {
+			misses += PULSE;
+			if (idx_hit >= 0)
+				cpu_data->states[idx_hit].early_hits += PULSE;
+		} else {
+			hits += PULSE;
+		}
+
+		cpu_data->states[idx_timer].misses = misses;
+		cpu_data->states[idx_timer].hits = hits;
+	}
+
+	/*
+	 * If the total time span between idle state selection and the "reflect"
+	 * callback is greater than or equal to the sleep length determined at
+	 * the idle state selection time, the wakeup is likely to be due to a
+	 * timer event.
+	 */
+	if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns)
+		measured_us = UINT_MAX;
+
+	/*
+	 * Save idle duration values corresponding to non-timer wakeups for
+	 * pattern detection.
+	 */
+	cpu_data->intervals[cpu_data->interval_idx++] = measured_us;
+	if (cpu_data->interval_idx > INTERVALS)
+		cpu_data->interval_idx = 0;
+}
+
+/**
+ * teo_find_shallower_state - Find shallower idle state matching given duration.
+ * @drv: cpuidle driver containing state data.
+ * @dev: Target CPU.
+ * @state_idx: Index of the capping idle state.
+ * @duration_us: Idle duration value to match.
+ */
+static int teo_find_shallower_state(struct cpuidle_driver *drv,
+				    struct cpuidle_device *dev, int state_idx,
+				    unsigned int duration_us)
+{
+	int i;
+
+	for (i = state_idx - 1; i >= 0; i--) {
+		if (drv->states[i].disabled || dev->states_usage[i].disable)
+			continue;
+
+		state_idx = i;
+		if (drv->states[i].target_residency <= duration_us)
+			break;
+	}
+	return state_idx;
+}
+
+/**
+ * teo_select - Selects the next idle state to enter.
+ * @drv: cpuidle driver containing state data.
+ * @dev: Target CPU.
+ * @stop_tick: Indication on whether or not to stop the scheduler tick.
+ */
+static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
+		      bool *stop_tick)
+{
+	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
+	int latency_req = cpuidle_governor_latency_req(dev->cpu);
+	unsigned int duration_us, count;
+	int max_early_idx, idx, i;
+	ktime_t delta_tick;
+
+	if (cpu_data->last_state >= 0) {
+		teo_update(drv, dev);
+		cpu_data->last_state = -1;
+	}
+
+	cpu_data->time_span_ns = local_clock();
+
+	cpu_data->sleep_length_ns = tick_nohz_get_sleep_length(&delta_tick);
+	duration_us = ktime_to_us(cpu_data->sleep_length_ns);
+
+	count = 0;
+	max_early_idx = -1;
+	idx = -1;
+
+	for (i = 0; i < drv->state_count; i++) {
+		struct cpuidle_state *s = &drv->states[i];
+		struct cpuidle_state_usage *su = &dev->states_usage[i];
+
+		if (s->disabled || su->disable) {
+			/*
+			 * If the "early hits" metric of a disabled state is
+			 * greater than the current maximum, it should be taken
+			 * into account, because it would be a mistake to select
+			 * a deeper state with lower "early hits" metric.  The
+			 * index cannot be changed to point to it, however, so
+			 * just increase the max count alone and let the index
+			 * still point to a shallower idle state.
+			 */
+			if (max_early_idx >= 0 &&
+			    count < cpu_data->states[i].early_hits)
+				count = cpu_data->states[i].early_hits;
+
+			continue;
+		}
+
+		if (idx < 0)
+			idx = i; /* first enabled state */
+
+		if (s->target_residency > duration_us)
+			break;
+
+		if (s->exit_latency > latency_req) {
+			/*
+			 * If we break out of the loop for latency reasons, use
+			 * the target residency of the selected state as the
+			 * expected idle duration to avoid stopping the tick
+			 * as long as that target residency is low enough.
+			 */
+			duration_us = drv->states[idx].target_residency;
+			goto refine;
+		}
+
+		idx = i;
+
+		if (count < cpu_data->states[i].early_hits &&
+		    !(tick_nohz_tick_stopped() &&
+		      drv->states[i].target_residency < TICK_USEC)) {
+			count = cpu_data->states[i].early_hits;
+			max_early_idx = i;
+		}
+	}
+
+	/*
+	 * If the "hits" metric of the idle state matching the sleep length is
+	 * greater than its "misses" metric, that is the one to use.  Otherwise,
+	 * it is more likely that one of the shallower states will match the
+	 * idle duration observed after wakeup, so take the one with the maximum
+	 * "early hits" metric, but if that cannot be determined, just use the
+	 * state selected so far.
+	 */
+	if (cpu_data->states[idx].hits <= cpu_data->states[idx].misses &&
+	    max_early_idx >= 0) {
+		idx = max_early_idx;
+		duration_us = drv->states[idx].target_residency;
+	}
+
+refine:
+	if (idx < 0) {
+		idx = 0; /* No states enabled. Must use 0. */
+	} else if (idx > 0) {
+		u64 sum = 0;
+
+		count = 0;
+
+		/*
+		 * Count and sum the most recent idle duration values less than
+		 * the target residency of the state selected so far, find the
+		 * max.
+		 */
+		for (i = 0; i < INTERVALS; i++) {
+			unsigned int val = cpu_data->intervals[i];
+
+			if (val >= drv->states[idx].target_residency)
+				continue;
+
+			count++;
+			sum += val;
+		}
+
+		/*
+		 * Give up unless the majority of the most recent idle duration
+		 * values are in the interesting range.
+		 */
+		if (count > INTERVALS / 2) {
+			unsigned int avg_us = div64_u64(sum, count);
+
+			/*
+			 * Avoid spending too much time in an idle state that
+			 * would be too shallow.
+			 */
+			if (!(tick_nohz_tick_stopped() && avg_us < TICK_USEC)) {
+				idx = teo_find_shallower_state(drv, dev, idx, avg_us);
+				duration_us = avg_us;
+			}
+		}
+	}
+
+	/*
+	 * Don't stop the tick if the selected state is a polling one or if the
+	 * expected idle duration is shorter than the tick period length.
+	 */
+	if (((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
+	    duration_us < TICK_USEC) && !tick_nohz_tick_stopped()) {
+		unsigned int delta_tick_us = ktime_to_us(delta_tick);
+
+		*stop_tick = false;
+
+		/*
+		 * The tick is not going to be stopped, so if the target
+		 * residency of the state to be returned is not within the time
+		 * till the closest timer including the tick, try to correct
+		 * that.
+		 */
+		if (idx > 0 && drv->states[idx].target_residency > delta_tick_us)
+			idx = teo_find_shallower_state(drv, dev, idx, delta_tick_us);
+	}
+
+	return idx;
+}
+
+/**
+ * teo_reflect - Note that governor data for the CPU need to be updated.
+ * @dev: Target CPU.
+ * @state: Entered state.
+ */
+static void teo_reflect(struct cpuidle_device *dev, int state)
+{
+	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
+
+	cpu_data->last_state = state;
+	/*
+	 * If the wakeup was not "natural", but triggered by one of the safety
+	 * nets, assume that the CPU might have been idle for the entire sleep
+	 * length time.
+	 */
+	if (dev->poll_time_limit ||
+	    (tick_nohz_idle_got_tick() && cpu_data->sleep_length_ns > TICK_NSEC)) {
+		dev->poll_time_limit = false;
+		cpu_data->time_span_ns = cpu_data->sleep_length_ns;
+	} else {
+		cpu_data->time_span_ns = local_clock() - cpu_data->time_span_ns;
+	}
+}
+
+/**
+ * teo_enable_device - Initialize the governor's data for the target CPU.
+ * @drv: cpuidle driver (not used).
+ * @dev: Target CPU.
+ */
+static int teo_enable_device(struct cpuidle_driver *drv,
+			     struct cpuidle_device *dev)
+{
+	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
+	int i;
+
+	memset(cpu_data, 0, sizeof(*cpu_data));
+
+	for (i = 0; i < INTERVALS; i++)
+		cpu_data->intervals[i] = UINT_MAX;
+
+	return 0;
+}
+
+static struct cpuidle_governor teo_governor = {
+	.name =		"teo",
+	.rating =	19,
+	.enable =	teo_enable_device,
+	.select =	teo_select,
+	.reflect =	teo_reflect,
+};
+
+static int __init teo_governor_init(void)
+{
+	return cpuidle_register_governor(&teo_governor);
+}
+
+postcore_initcall(teo_governor_init);