Merge branch 'work.regset' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

[linux/fpc-iii.git] / drivers / cpuidle / governors / teo.c

// 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.
 * @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 interval_idx;
        u64 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);
        int i, idx_hit = -1, idx_timer = -1;
        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;
        }

        /*
         * 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_ns <= cpu_data->sleep_length_ns) {
                        idx_timer = i;
                        if (drv->states[i].target_residency_ns <= measured_ns)
                                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;
        }

        /*
         * Save idle duration values corresponding to non-timer wakeups for
         * pattern detection.
         */
        cpu_data->intervals[cpu_data->interval_idx++] = measured_ns;
        if (cpu_data->interval_idx >= INTERVALS)
                cpu_data->interval_idx = 0;
}

static bool teo_time_ok(u64 interval_ns)
{
        return !tick_nohz_tick_stopped() || interval_ns >= TICK_NSEC;
}

/**
 * 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,
                                    u64 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);
        u64 duration_ns;
        unsigned int hits, misses, early_hits;
        int max_early_idx, prev_max_early_idx, constraint_idx, idx, i;
        ktime_t delta_tick;

        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;

        hits = 0;
        misses = 0;
        early_hits = 0;
        max_early_idx = -1;
        prev_max_early_idx = -1;
        constraint_idx = drv->state_count;
        idx = -1;

        for (i = 0; i < drv->state_count; i++) {
                struct cpuidle_state *s = &drv->states[i];

                if (dev->states_usage[i].disable) {
                        /*
                         * Ignore disabled states with target residencies beyond
                         * the anticipated idle duration.
                         */
                        if (s->target_residency_ns > duration_ns)
                                continue;

                        /*
                         * This state is disabled, so the range of idle duration
                         * values corresponding to it is covered by the current
                         * candidate state, but still the "hits" and "misses"
                         * metrics of the disabled state need to be used to
                         * decide whether or not the state covering the range in
                         * question is good enough.
                         */
                        hits = cpu_data->states[i].hits;
                        misses = cpu_data->states[i].misses;

                        if (early_hits >= cpu_data->states[i].early_hits ||
                            idx < 0)
                                continue;

                        /*
                         * If the current candidate state has been the one with
                         * the maximum "early hits" metric so far, the "early
                         * hits" metric of the disabled state replaces the
                         * current "early hits" count to avoid selecting a
                         * deeper state with lower "early hits" metric.
                         */
                        if (max_early_idx == idx) {
                                early_hits = cpu_data->states[i].early_hits;
                                continue;
                        }

                        /*
                         * The current candidate state is closer to the disabled
                         * one than the current maximum "early hits" state, so
                         * replace the latter with it, but in case the maximum
                         * "early hits" state index has not been set so far,
                         * check if the current candidate state is not too
                         * shallow for that role.
                         */
                        if (teo_time_ok(drv->states[idx].target_residency_ns)) {
                                prev_max_early_idx = max_early_idx;
                                early_hits = cpu_data->states[i].early_hits;
                                max_early_idx = idx;
                        }

                        continue;
                }

                if (idx < 0) {
                        idx = i; /* first enabled state */
                        hits = cpu_data->states[i].hits;
                        misses = cpu_data->states[i].misses;
                }

                if (s->target_residency_ns > duration_ns)
                        break;

                if (s->exit_latency_ns > latency_req && constraint_idx > i)
                        constraint_idx = i;

                idx = i;
                hits = cpu_data->states[i].hits;
                misses = cpu_data->states[i].misses;

                if (early_hits < cpu_data->states[i].early_hits &&
                    teo_time_ok(drv->states[i].target_residency_ns)) {
                        prev_max_early_idx = max_early_idx;
                        early_hits = 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 (hits <= misses) {
                /*
                 * The current candidate state is not suitable, so take the one
                 * whose "early hits" metric is the maximum for the range of
                 * shallower states.
                 */
                if (idx == max_early_idx)
                        max_early_idx = prev_max_early_idx;

                if (max_early_idx >= 0) {
                        idx = max_early_idx;
                        duration_ns = drv->states[idx].target_residency_ns;
                }
        }

        /*
         * If there is a latency constraint, it may be necessary to use a
         * shallower idle state than the one selected so far.
         */
        if (constraint_idx < idx)
                idx = constraint_idx;

        if (idx < 0) {
                idx = 0; /* No states enabled. Must use 0. */
        } else if (idx > 0) {
                unsigned int count = 0;
                u64 sum = 0;

                /*
                 * Count and sum the most recent idle duration values less than
                 * the current expected idle duration value.
                 */
                for (i = 0; i < INTERVALS; i++) {
                        u64 val = cpu_data->intervals[i];

                        if (val >= duration_ns)
                                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) {
                        u64 avg_ns = div64_u64(sum, count);

                        /*
                         * Avoid spending too much time in an idle state that
                         * would be too shallow.
                         */
                        if (teo_time_ok(avg_ns)) {
                                duration_ns = avg_ns;
                                if (drv->states[idx].target_residency_ns > avg_ns)
                                        idx = teo_find_shallower_state(drv, dev,
                                                                       idx, avg_ns);
                        }
                }
        }

        /*
         * 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 > 0 && 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 < INTERVALS; i++)
                cpu_data->intervals[i] = U64_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);