and that is the primary reason for having more than one governor in the
``CPUIdle`` subsystem.
-There are two ``CPUIdle`` governors available, ``menu`` and ``ladder``. Which
-of them is used depends on the configuration of the kernel and in particular on
-whether or not the scheduler tick can be `stopped by the idle
-loop <idle-cpus-and-tick_>`_. It is possible to change the governor at run time
-if the ``cpuidle_sysfs_switch`` command line parameter has been passed to the
-kernel, but that is not safe in general, so it should not be done on production
-systems (that may change in the future, though). The name of the ``CPUIdle``
-governor currently used by the kernel can be read from the
+There are three ``CPUIdle`` governors available, ``menu``, `TEO <teo-gov_>`_
+and ``ladder``. Which of them is used by default depends on the configuration
+of the kernel and in particular on whether or not the scheduler tick can be
+`stopped by the idle loop <idle-cpus-and-tick_>`_. It is possible to change the
+governor at run time if the ``cpuidle_sysfs_switch`` command line parameter has
+been passed to the kernel, but that is not safe in general, so it should not be
+done on production systems (that may change in the future, though). The name of
+the ``CPUIdle`` governor currently used by the kernel can be read from the
:file:`current_governor_ro` (or :file:`current_governor` if
``cpuidle_sysfs_switch`` is present in the kernel command line) file under
:file:`/sys/devices/system/cpu/cpuidle/` in ``sysfs``.
``CPUIdle`` governor on it will be ``ladder``.
+.. _menu-gov:
+
The ``menu`` Governor
=====================
target residency.
+.. _teo-gov:
+
+The Timer Events Oriented (TEO) Governor
+========================================
+
+The timer events oriented (TEO) governor is an alternative ``CPUIdle`` governor
+for tickless systems. It follows the same basic strategy as the ``menu`` `one
+<menu-gov_>`_: it always tries to find the deepest idle state suitable for the
+given conditions. However, it applies a different approach to that problem.
+
+First, it does not use sleep length correction factors, but instead it attempts
+to correlate the observed idle duration values with the available idle states
+and use that information to pick up the idle state that is most likely to
+"match" the upcoming CPU idle interval. Second, it does not take the tasks
+that were running on the given CPU in the past and are waiting on some I/O
+operations to complete now at all (there is no guarantee that they will run on
+the same CPU when they become runnable again) and the pattern detection code in
+it avoids taking timer wakeups into account. It also only uses idle duration
+values less than the current time till the closest timer (with the scheduler
+tick excluded) for that purpose.
+
+Like in the ``menu`` governor `case <menu-gov_>`_, the first step is to obtain
+the *sleep length*, which is the time until the closest timer event with the
+assumption that the scheduler tick will be stopped (that also is the upper bound
+on the time until the next CPU wakeup). That value is then used to preselect an
+idle state on the basis of three metrics maintained for each idle state provided
+by the ``CPUIdle`` driver: ``hits``, ``misses`` and ``early_hits``.
+
+The ``hits`` and ``misses`` metrics measure the likelihood that a given idle
+state will "match" the observed (post-wakeup) idle duration if it "matches" the
+sleep length. They both are subject to decay (after a CPU wakeup) every time
+the target residency of the idle state corresponding to them is less than or
+equal to the sleep length and the target residency of the next idle state is
+greater than the sleep length (that is, when the idle state corresponding to
+them "matches" the sleep length). The ``hits`` metric is increased if the
+former condition is satisfied and the target residency of the given idle state
+is less than or equal to the observed idle duration and the target residency of
+the next idle state is greater than the observed idle duration at the same time
+(that is, it is increased when the given idle state "matches" both the sleep
+length and the observed idle duration). In turn, the ``misses`` metric is
+increased when the given idle state "matches" the sleep length only and the
+observed idle duration is too short for its target residency.
+
+The ``early_hits`` metric measures the likelihood that a given idle state will
+"match" the observed (post-wakeup) idle duration if it does not "match" the
+sleep length. It is subject to decay on every CPU wakeup and it is increased
+when the idle state corresponding to it "matches" the observed (post-wakeup)
+idle duration and the target residency of the next idle state is less than or
+equal to the sleep length (i.e. the idle state "matching" the sleep length is
+deeper than the given one).
+
+The governor walks the list of idle states provided by the ``CPUIdle`` driver
+and finds the last (deepest) one with the target residency less than or equal
+to the sleep length. Then, the ``hits`` and ``misses`` metrics of that idle
+state are compared with each other and it is preselected if the ``hits`` one is
+greater (which means that that idle state is likely to "match" the observed idle
+duration after CPU wakeup). If the ``misses`` one is greater, the governor
+preselects the shallower idle state with the maximum ``early_hits`` metric
+(or if there are multiple shallower idle states with equal ``early_hits``
+metric which also is the maximum, the shallowest of them will be preselected).
+[If there is a wakeup latency constraint coming from the `PM QoS framework
+<cpu-pm-qos_>`_ which is hit before reaching the deepest idle state with the
+target residency within the sleep length, the deepest idle state with the exit
+latency within the constraint is preselected without consulting the ``hits``,
+``misses`` and ``early_hits`` metrics.]
+
+Next, the governor takes several idle duration values observed most recently
+into consideration and if at least a half of them are greater than or equal to
+the target residency of the preselected idle state, that idle state becomes the
+final candidate to ask for. Otherwise, the average of the most recent idle
+duration values below the target residency of the preselected idle state is
+computed and the governor walks the idle states shallower than the preselected
+one and finds the deepest of them with the target residency within that average.
+That idle state is then taken as the final candidate to ask for.
+
+Still, at this point the governor may need to refine the idle state selection if
+it has not decided to `stop the scheduler tick <idle-cpus-and-tick_>`_. That
+generally happens if the target residency of the idle state selected so far is
+less than the tick period and the tick has not been stopped already (in a
+previous iteration of the idle loop). Then, like in the ``menu`` governor
+`case <menu-gov_>`_, the sleep length used in the previous computations may not
+reflect the real time until the closest timer event and if it really is greater
+than that time, a shallower state with a suitable target residency may need to
+be selected.
+
+
.. _idle-states-representation:
Representation of Idle States
--- /dev/null
+// 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);
projects / openwrt / staging / blogic.git / commitdiff