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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /drivers/cpuidle/governors/teo.c
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'drivers/cpuidle/governors/teo.c')
-rw-r--r--drivers/cpuidle/governors/teo.c534
1 files changed, 534 insertions, 0 deletions
diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
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+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Timer events oriented CPU idle governor
+ *
+ * Copyright (C) 2018 - 2021 Intel Corporation
+ * Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+ */
+
+/**
+ * DOC: teo-description
+ *
+ * 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 cause 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 (known) time till the closest
+ * timer event, referred to as the sleep length, is likely to be suitable for
+ * the upcoming CPU idle period and, if not, then which of the shallower idle
+ * states to choose instead of it.
+ *
+ * Of course, non-timer wakeup sources are more important in some use cases
+ * which can be covered by taking a few most recent idle time intervals of the
+ * CPU into account. However, even in that context it is not necessary to
+ * consider idle duration values greater than the sleep length, because the
+ * closest timer will ultimately wake up the CPU anyway unless it is woken up
+ * earlier.
+ *
+ * Thus this governor estimates whether or not the prospective idle duration of
+ * a CPU is likely to be significantly shorter than the sleep length and selects
+ * an idle state for it accordingly.
+ *
+ * The computations carried out by this governor are based on using bins whose
+ * boundaries are aligned with the target residency parameter values of the CPU
+ * idle states provided by the %CPUIdle driver in the ascending order. That is,
+ * the first bin spans from 0 up to, but not including, the target residency of
+ * the second idle state (idle state 1), the second bin spans from the target
+ * residency of idle state 1 up to, but not including, the target residency of
+ * idle state 2, the third bin spans from the target residency of idle state 2
+ * up to, but not including, the target residency of idle state 3 and so on.
+ * The last bin spans from the target residency of the deepest idle state
+ * supplied by the driver to infinity.
+ *
+ * Two metrics called "hits" and "intercepts" are associated with each bin.
+ * They are updated every time before selecting an idle state for the given CPU
+ * in accordance with what happened last time.
+ *
+ * The "hits" metric reflects the relative frequency of situations in which the
+ * sleep length and the idle duration measured after CPU wakeup fall into the
+ * same bin (that is, the CPU appears to wake up "on time" relative to the sleep
+ * length). In turn, the "intercepts" metric reflects the relative frequency of
+ * situations in which the measured idle duration is so much shorter than the
+ * sleep length that the bin it falls into corresponds to an idle state
+ * shallower than the one whose bin is fallen into by the sleep length (these
+ * situations are referred to as "intercepts" below).
+ *
+ * In addition to the metrics described above, the governor counts recent
+ * intercepts (that is, intercepts that have occurred during the last
+ * %NR_RECENT invocations of it for the given CPU) for each bin.
+ *
+ * In order to select an idle state for a CPU, the governor takes the following
+ * steps (modulo the possible latency constraint that must be taken into account
+ * too):
+ *
+ * 1. Find the deepest CPU idle state whose target residency does not exceed
+ * the current sleep length (the candidate idle state) and compute 3 sums as
+ * follows:
+ *
+ * - The sum of the "hits" and "intercepts" metrics for the candidate state
+ * and all of the deeper idle states (it represents the cases in which the
+ * CPU was idle long enough to avoid being intercepted if the sleep length
+ * had been equal to the current one).
+ *
+ * - The sum of the "intercepts" metrics for all of the idle states shallower
+ * than the candidate one (it represents the cases in which the CPU was not
+ * idle long enough to avoid being intercepted if the sleep length had been
+ * equal to the current one).
+ *
+ * - The sum of the numbers of recent intercepts for all of the idle states
+ * shallower than the candidate one.
+ *
+ * 2. If the second sum is greater than the first one or the third sum is
+ * greater than %NR_RECENT / 2, the CPU is likely to wake up early, so look
+ * for an alternative idle state to select.
+ *
+ * - Traverse the idle states shallower than the candidate one in the
+ * descending order.
+ *
+ * - For each of them compute the sum of the "intercepts" metrics and the sum
+ * of the numbers of recent intercepts over all of the idle states between
+ * it and the candidate one (including the former and excluding the
+ * latter).
+ *
+ * - If each of these sums that needs to be taken into account (because the
+ * check related to it has indicated that the CPU is likely to wake up
+ * early) is greater than a half of the corresponding sum computed in step
+ * 1 (which means that the target residency of the state in question had
+ * not exceeded the idle duration in over a half of the relevant cases),
+ * select the given idle state instead of the candidate one.
+ *
+ * 3. By default, select the candidate state.
+ */
+
+#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 recent early wakeup patterns.
+ */
+#define NR_RECENT 9
+
+/**
+ * struct teo_bin - Metrics used by the TEO cpuidle governor.
+ * @intercepts: The "intercepts" metric.
+ * @hits: The "hits" metric.
+ * @recent: The number of recent "intercepts".
+ */
+struct teo_bin {
+ unsigned int intercepts;
+ unsigned int hits;
+ unsigned int recent;
+};
+
+/**
+ * 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).
+ * @state_bins: Idle state data bins for this CPU.
+ * @total: Grand total of the "intercepts" and "hits" mertics for all bins.
+ * @next_recent_idx: Index of the next @recent_idx entry to update.
+ * @recent_idx: Indices of bins corresponding to recent "intercepts".
+ */
+struct teo_cpu {
+ s64 time_span_ns;
+ s64 sleep_length_ns;
+ struct teo_bin state_bins[CPUIDLE_STATE_MAX];
+ unsigned int total;
+ int next_recent_idx;
+ int recent_idx[NR_RECENT];
+};
+
+static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
+
+/**
+ * teo_update - Update CPU metrics 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);
+ int i, idx_timer = 0, idx_duration = 0;
+ u64 measured_ns;
+
+ if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) {
+ /*
+ * One of the safety nets has triggered or the wakeup was close
+ * enough to the closest timer event expected at the idle state
+ * selection time to be discarded.
+ */
+ measured_ns = U64_MAX;
+ } else {
+ u64 lat_ns = drv->states[dev->last_state_idx].exit_latency_ns;
+
+ /*
+ * The computations below are to determine whether or not the
+ * (saved) time till the next timer event and the measured idle
+ * duration fall into the same "bin", so use last_residency_ns
+ * for that instead of time_span_ns which includes the cpuidle
+ * overhead.
+ */
+ measured_ns = dev->last_residency_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_ns >= lat_ns)
+ measured_ns -= lat_ns / 2;
+ else
+ measured_ns /= 2;
+ }
+
+ cpu_data->total = 0;
+
+ /*
+ * Decay the "hits" and "intercepts" metrics for all of the bins and
+ * find the bins that the sleep length and the measured idle duration
+ * fall into.
+ */
+ for (i = 0; i < drv->state_count; i++) {
+ s64 target_residency_ns = drv->states[i].target_residency_ns;
+ struct teo_bin *bin = &cpu_data->state_bins[i];
+
+ bin->hits -= bin->hits >> DECAY_SHIFT;
+ bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
+
+ cpu_data->total += bin->hits + bin->intercepts;
+
+ if (target_residency_ns <= cpu_data->sleep_length_ns) {
+ idx_timer = i;
+ if (target_residency_ns <= measured_ns)
+ idx_duration = i;
+ }
+ }
+
+ i = cpu_data->next_recent_idx++;
+ if (cpu_data->next_recent_idx >= NR_RECENT)
+ cpu_data->next_recent_idx = 0;
+
+ if (cpu_data->recent_idx[i] >= 0)
+ cpu_data->state_bins[cpu_data->recent_idx[i]].recent--;
+
+ /*
+ * If the measured idle duration falls into the same bin as the sleep
+ * length, this is a "hit", so update the "hits" metric for that bin.
+ * Otherwise, update the "intercepts" metric for the bin fallen into by
+ * the measured idle duration.
+ */
+ if (idx_timer == idx_duration) {
+ cpu_data->state_bins[idx_timer].hits += PULSE;
+ cpu_data->recent_idx[i] = -1;
+ } else {
+ cpu_data->state_bins[idx_duration].intercepts += PULSE;
+ cpu_data->state_bins[idx_duration].recent++;
+ cpu_data->recent_idx[i] = idx_duration;
+ }
+
+ cpu_data->total += PULSE;
+}
+
+static bool teo_time_ok(u64 interval_ns)
+{
+ return !tick_nohz_tick_stopped() || interval_ns >= TICK_NSEC;
+}
+
+static s64 teo_middle_of_bin(int idx, struct cpuidle_driver *drv)
+{
+ return (drv->states[idx].target_residency_ns +
+ drv->states[idx+1].target_residency_ns) / 2;
+}
+
+/**
+ * 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_ns: Idle duration value to match.
+ */
+static int teo_find_shallower_state(struct cpuidle_driver *drv,
+ struct cpuidle_device *dev, int state_idx,
+ s64 duration_ns)
+{
+ int i;
+
+ for (i = state_idx - 1; i >= 0; i--) {
+ if (dev->states_usage[i].disable)
+ continue;
+
+ state_idx = i;
+ if (drv->states[i].target_residency_ns <= duration_ns)
+ 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);
+ s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
+ unsigned int idx_intercept_sum = 0;
+ unsigned int intercept_sum = 0;
+ unsigned int idx_recent_sum = 0;
+ unsigned int recent_sum = 0;
+ unsigned int idx_hit_sum = 0;
+ unsigned int hit_sum = 0;
+ int constraint_idx = 0;
+ int idx0 = 0, idx = -1;
+ bool alt_intercepts, alt_recent;
+ ktime_t delta_tick;
+ s64 duration_ns;
+ int i;
+
+ if (dev->last_state_idx >= 0) {
+ teo_update(drv, dev);
+ dev->last_state_idx = -1;
+ }
+
+ cpu_data->time_span_ns = local_clock();
+
+ duration_ns = tick_nohz_get_sleep_length(&delta_tick);
+ cpu_data->sleep_length_ns = duration_ns;
+
+ /* Check if there is any choice in the first place. */
+ if (drv->state_count < 2) {
+ idx = 0;
+ goto end;
+ }
+ if (!dev->states_usage[0].disable) {
+ idx = 0;
+ if (drv->states[1].target_residency_ns > duration_ns)
+ goto end;
+ }
+
+ /*
+ * Find the deepest idle state whose target residency does not exceed
+ * the current sleep length and the deepest idle state not deeper than
+ * the former whose exit latency does not exceed the current latency
+ * constraint. Compute the sums of metrics for early wakeup pattern
+ * detection.
+ */
+ for (i = 1; i < drv->state_count; i++) {
+ struct teo_bin *prev_bin = &cpu_data->state_bins[i-1];
+ struct cpuidle_state *s = &drv->states[i];
+
+ /*
+ * Update the sums of idle state mertics for all of the states
+ * shallower than the current one.
+ */
+ intercept_sum += prev_bin->intercepts;
+ hit_sum += prev_bin->hits;
+ recent_sum += prev_bin->recent;
+
+ if (dev->states_usage[i].disable)
+ continue;
+
+ if (idx < 0) {
+ idx = i; /* first enabled state */
+ idx0 = i;
+ }
+
+ if (s->target_residency_ns > duration_ns)
+ break;
+
+ idx = i;
+
+ if (s->exit_latency_ns <= latency_req)
+ constraint_idx = i;
+
+ idx_intercept_sum = intercept_sum;
+ idx_hit_sum = hit_sum;
+ idx_recent_sum = recent_sum;
+ }
+
+ /* Avoid unnecessary overhead. */
+ if (idx < 0) {
+ idx = 0; /* No states enabled, must use 0. */
+ goto end;
+ } else if (idx == idx0) {
+ goto end;
+ }
+
+ /*
+ * If the sum of the intercepts metric for all of the idle states
+ * shallower than the current candidate one (idx) is greater than the
+ * sum of the intercepts and hits metrics for the candidate state and
+ * all of the deeper states, or the sum of the numbers of recent
+ * intercepts over all of the states shallower than the candidate one
+ * is greater than a half of the number of recent events taken into
+ * account, the CPU is likely to wake up early, so find an alternative
+ * idle state to select.
+ */
+ alt_intercepts = 2 * idx_intercept_sum > cpu_data->total - idx_hit_sum;
+ alt_recent = idx_recent_sum > NR_RECENT / 2;
+ if (alt_recent || alt_intercepts) {
+ s64 first_suitable_span_ns = duration_ns;
+ int first_suitable_idx = idx;
+
+ /*
+ * Look for the deepest idle state whose target residency had
+ * not exceeded the idle duration in over a half of the relevant
+ * cases (both with respect to intercepts overall and with
+ * respect to the recent intercepts only) in the past.
+ *
+ * Take the possible latency constraint and duration limitation
+ * present if the tick has been stopped already into account.
+ */
+ intercept_sum = 0;
+ recent_sum = 0;
+
+ for (i = idx - 1; i >= 0; i--) {
+ struct teo_bin *bin = &cpu_data->state_bins[i];
+ s64 span_ns;
+
+ intercept_sum += bin->intercepts;
+ recent_sum += bin->recent;
+
+ span_ns = teo_middle_of_bin(i, drv);
+
+ if ((!alt_recent || 2 * recent_sum > idx_recent_sum) &&
+ (!alt_intercepts ||
+ 2 * intercept_sum > idx_intercept_sum)) {
+ if (teo_time_ok(span_ns) &&
+ !dev->states_usage[i].disable) {
+ idx = i;
+ duration_ns = span_ns;
+ } else {
+ /*
+ * The current state is too shallow or
+ * disabled, so take the first enabled
+ * deeper state with suitable time span.
+ */
+ idx = first_suitable_idx;
+ duration_ns = first_suitable_span_ns;
+ }
+ break;
+ }
+
+ if (dev->states_usage[i].disable)
+ continue;
+
+ if (!teo_time_ok(span_ns)) {
+ /*
+ * The current state is too shallow, but if an
+ * alternative candidate state has been found,
+ * it may still turn out to be a better choice.
+ */
+ if (first_suitable_idx != idx)
+ continue;
+
+ break;
+ }
+
+ first_suitable_span_ns = span_ns;
+ first_suitable_idx = i;
+ }
+ }
+
+ /*
+ * If there is a latency constraint, it may be necessary to select an
+ * idle state shallower than the current candidate one.
+ */
+ if (idx > constraint_idx)
+ idx = constraint_idx;
+
+end:
+ /*
+ * 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_ns < TICK_NSEC) && !tick_nohz_tick_stopped()) {
+ *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 > idx0 &&
+ drv->states[idx].target_residency_ns > delta_tick)
+ idx = teo_find_shallower_state(drv, dev, idx, delta_tick);
+ }
+
+ 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);
+
+ dev->last_state_idx = 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 < NR_RECENT; i++)
+ cpu_data->recent_idx[i] = -1;
+
+ 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);