diff options
Diffstat (limited to 'drivers/cpuidle/governors/teo.c')
| -rw-r--r-- | drivers/cpuidle/governors/teo.c | 470 |
1 files changed, 236 insertions, 234 deletions
diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c index d9262db79cae..81ac5fd58a1c 100644 --- a/drivers/cpuidle/governors/teo.c +++ b/drivers/cpuidle/governors/teo.c @@ -10,25 +10,27 @@ * 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. + * timer interrupts are two or more orders of magnitude more frequent than any + * other interrupt types, so they are likely to dominate CPU wakeup patterns. + * Moreover, in principle, the time when the next timer event is going to occur + * can be determined at the idle state selection time, although doing that may + * be costly, so it can be regarded as the most reliable source of information + * for idle state selection. * - * 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. + * Of course, non-timer wakeup sources are more important in some use cases, + * but even then it is generally unnecessary to consider idle duration values + * greater than the time till the next timer event, referred as the sleep + * length in what follows, 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. + * However, since obtaining the sleep length may be costly, the governor first + * checks if it can select a shallow idle state using wakeup pattern information + * from recent times, in which case it can do without knowing the sleep length + * at all. For this purpose, it counts CPU wakeup events and looks for an idle + * state whose target residency has not exceeded the idle duration (measured + * after wakeup) in the majority of relevant recent cases. If the target + * residency of that state is small enough, it may be used right away and the + * sleep length need not be determined. * * 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 @@ -49,56 +51,50 @@ * 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). + * non-timer wakeup events for which the measured idle duration falls into a bin + * that corresponds to an idle state shallower than the one whose bin is fallen + * into by the sleep length (these events are also 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. + * The governor also counts "intercepts" with the measured idle duration below + * the tick period length and uses this information when deciding whether or not + * to stop the scheduler tick. * * 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: + * 1. Find the deepest enabled CPU idle state (the candidate idle state) and + * compute 2 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 "hits" metric for all of the idle states shallower than + * the candidate one (it represents the cases in which the CPU was likely + * woken up by a timer). * - * - 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 "intercepts" metric for all of the idle states shallower + * than the candidate one (it represents the cases in which the CPU was + * likely woken up by a non-timer wakeup source). * - * - The sum of the numbers of recent intercepts for all of the idle states - * shallower than the candidate one. + * 2. If the second sum computed in step 1 is greater than a half of the sum of + * both metrics for the candidate state bin and all subsequent bins (if any), + * a shallower idle state is likely to be more suitable, so look for it. * - * 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 + * - Traverse the enabled 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). + * - For each of them compute the sum of the "intercepts" metrics over all + * of the idle states between it and the candidate one (including the + * former and excluding the latter). + * + * - If this sum is greater than a half of the second sum computed in step 1, + * use the given idle state as the new candidate one. * - * - 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. If the current candidate state is state 0 or its target residency is short + * enough, return it and prevent the scheduler tick from being stopped. * - * 3. By default, select the candidate state. + * 4. Obtain the sleep length value and check if it is below the target + * residency of the current candidate state, in which case a new shallower + * candidate state needs to be found, so look for it. */ #include <linux/cpuidle.h> @@ -107,6 +103,14 @@ #include <linux/sched/clock.h> #include <linux/tick.h> +#include "gov.h" + +/* + * Idle state exit latency threshold used for deciding whether or not to check + * the time till the closest expected timer event. + */ +#define LATENCY_THRESHOLD_NS (RESIDENCY_THRESHOLD_NS / 2) + /* * The PULSE value is added to metrics when they grow and the DECAY_SHIFT value * is used for decreasing metrics on a regular basis. @@ -114,44 +118,48 @@ #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". + * @total: Grand total of the "intercepts" and "hits" metrics for all bins. + * @total_tick: Wakeups by the scheduler tick. + * @tick_intercepts: "Intercepts" before TICK_NSEC. + * @short_idles: Wakeups after short idle periods. + * @tick_wakeup: Set if the last wakeup was by the scheduler tick. */ 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]; + unsigned int total_tick; + unsigned int tick_intercepts; + unsigned int short_idles; + bool tick_wakeup; }; static DEFINE_PER_CPU(struct teo_cpu, teo_cpus); +static void teo_decay(unsigned int *metric) +{ + unsigned int delta = *metric >> DECAY_SHIFT; + + if (delta) + *metric -= delta; + else + *metric = 0; +} + /** * teo_update - Update CPU metrics after wakeup. * @drv: cpuidle driver containing state data. @@ -159,27 +167,23 @@ static DEFINE_PER_CPU(struct teo_cpu, teo_cpus); */ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev) { - struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu); + struct teo_cpu *cpu_data = this_cpu_ptr(&teo_cpus); int i, idx_timer = 0, idx_duration = 0; - u64 measured_ns; + s64 target_residency_ns, measured_ns; + unsigned int total = 0; - if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) { + teo_decay(&cpu_data->short_idles); + + if (dev->poll_time_limit) { + dev->poll_time_limit = false; /* - * 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. + * Polling state timeout has triggered, so assume that this + * might have been a long sleep. */ - measured_ns = U64_MAX; + measured_ns = S64_MAX; } else { - u64 lat_ns = drv->states[dev->last_state_idx].exit_latency_ns; + s64 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 @@ -187,27 +191,30 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev) * time, so take 1/2 of the exit latency as a very rough * approximation of the average of it. */ - if (measured_ns >= lat_ns) + if (measured_ns >= lat_ns) { measured_ns -= lat_ns / 2; - else + if (measured_ns < RESIDENCY_THRESHOLD_NS) + cpu_data->short_idles += PULSE; + } else { measured_ns /= 2; + cpu_data->short_idles += PULSE; + } } - 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; + teo_decay(&bin->hits); + total += bin->hits; + teo_decay(&bin->intercepts); + total += bin->intercepts; - cpu_data->total += bin->hits + bin->intercepts; + target_residency_ns = drv->states[i].target_residency_ns; if (target_residency_ns <= cpu_data->sleep_length_ns) { idx_timer = i; @@ -216,12 +223,23 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev) } } - i = cpu_data->next_recent_idx++; - if (cpu_data->next_recent_idx >= NR_RECENT) - cpu_data->next_recent_idx = 0; + cpu_data->total = total + PULSE; - if (cpu_data->recent_idx[i] >= 0) - cpu_data->state_bins[cpu_data->recent_idx[i]].recent--; + teo_decay(&cpu_data->tick_intercepts); + + teo_decay(&cpu_data->total_tick); + if (cpu_data->tick_wakeup) { + cpu_data->total_tick += PULSE; + /* + * If tick wakeups dominate the wakeup pattern, count this one + * as a hit on the deepest available idle state to increase the + * likelihood of stopping the tick. + */ + if (3 * cpu_data->total_tick > 2 * cpu_data->total) { + cpu_data->state_bins[drv->state_count-1].hits += PULSE; + return; + } + } /* * If the measured idle duration falls into the same bin as the sleep @@ -231,25 +249,11 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev) */ 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; + if (measured_ns <= TICK_NSEC) + cpu_data->tick_intercepts += PULSE; } - - 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; } /** @@ -285,18 +289,15 @@ static int teo_find_shallower_state(struct cpuidle_driver *drv, 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); + struct teo_cpu *cpu_data = this_cpu_ptr(&teo_cpus); s64 latency_req = cpuidle_governor_latency_req(dev->cpu); + ktime_t delta_tick = TICK_NSEC / 2; 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; @@ -305,67 +306,66 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *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; + /* + * Set the sleep length to infinity in case the invocation of + * tick_nohz_get_sleep_length() below is skipped, in which case it won't + * be known whether or not the subsequent wakeup is caused by a timer. + * It is generally fine to count the wakeup as an intercept then, except + * for the cases when the CPU is mostly woken up by timers and there may + * be opportunities to ask for a deeper idle state when no imminent + * timers are scheduled which may be missed. + */ + cpu_data->sleep_length_ns = KTIME_MAX; /* Check if there is any choice in the first place. */ if (drv->state_count < 2) { idx = 0; - goto end; + goto out_tick; } - if (!dev->states_usage[0].disable) { + + 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. - */ + /* 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 + * Update the sums of idle state metrics 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; + if (idx < 0) + idx0 = i; /* first enabled state */ idx = i; if (s->exit_latency_ns <= latency_req) constraint_idx = i; + /* Save the sums for the current state. */ 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 out_tick; + } + + if (idx == idx0) { + /* + * Only one idle state is enabled, so use it, but do not + * allow the tick to be stopped it is shallow enough. + */ + duration_ns = drv->states[idx].target_residency_ns; goto end; } @@ -373,75 +373,40 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, * 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. + * all of the deeper states, a shallower idle state is likely to be a + * better choice. */ - 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; + if (2 * idx_intercept_sum > cpu_data->total - idx_hit_sum) { + int min_idx = idx0; + + if (tick_nohz_tick_stopped()) { + /* + * Look for the shallowest idle state below the current + * candidate one whose target residency is at least + * equal to the tick period length. + */ + while (min_idx < idx && + drv->states[min_idx].target_residency_ns < TICK_NSEC) + min_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. + * cases in the past. * - * Take the possible latency constraint and duration limitation - * present if the tick has been stopped already into account. + * Take the possible 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; - } + for (i = idx - 1, intercept_sum = 0; i >= min_idx; i--) { + intercept_sum += cpu_data->state_bins[i].intercepts; 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; - + idx = i; + if (2 * intercept_sum > idx_intercept_sum) break; - } - - first_suitable_span_ns = span_ns; - first_suitable_idx = i; } } @@ -452,26 +417,77 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, if (idx > constraint_idx) idx = constraint_idx; + /* + * If either the candidate state is state 0 or its target residency is + * low enough, there is basically nothing more to do, but if the sleep + * length is not updated, the subsequent wakeup will be counted as an + * "intercept" which may be problematic in the cases when timer wakeups + * are dominant. Namely, it may effectively prevent deeper idle states + * from being selected at one point even if no imminent timers are + * scheduled. + * + * However, frequent timers in the RESIDENCY_THRESHOLD_NS range on one + * CPU are unlikely (user space has a default 50 us slack value for + * hrtimers and there are relatively few timers with a lower deadline + * value in the kernel), and even if they did happen, the potential + * benefit from using a deep idle state in that case would be + * questionable anyway for latency reasons. Thus if the measured idle + * duration falls into that range in the majority of cases, assume + * non-timer wakeups to be dominant and skip updating the sleep length + * to reduce latency. + * + * Also, if the latency constraint is sufficiently low, it will force + * shallow idle states regardless of the wakeup type, so the sleep + * length need not be known in that case. + */ + if ((!idx || drv->states[idx].target_residency_ns < RESIDENCY_THRESHOLD_NS) && + (2 * cpu_data->short_idles >= cpu_data->total || + latency_req < LATENCY_THRESHOLD_NS)) + goto out_tick; + + duration_ns = tick_nohz_get_sleep_length(&delta_tick); + cpu_data->sleep_length_ns = duration_ns; + + if (!idx) + goto out_tick; + + /* + * If the closest expected timer is before the target residency of the + * candidate state, a shallower one needs to be found. + */ + if (drv->states[idx].target_residency_ns > duration_ns) + idx = teo_find_shallower_state(drv, dev, idx, duration_ns); + + /* + * If the selected state's target residency is below the tick length + * and intercepts occurring before the tick length are the majority of + * total wakeup events, do not stop the tick. + */ + if (drv->states[idx].target_residency_ns < TICK_NSEC && + cpu_data->tick_intercepts > cpu_data->total / 2 + cpu_data->total / 8) + duration_ns = TICK_NSEC / 2; + 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. + * Allow the tick to be stopped unless the selected state is a polling + * one or 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; + if ((!(drv->states[idx].flags & CPUIDLE_FLAG_POLLING) && + duration_ns >= TICK_NSEC) || tick_nohz_tick_stopped()) + return idx; - /* - * 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); - } + /* + * 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); +out_tick: + *stop_tick = false; return idx; } @@ -482,21 +498,11 @@ end: */ static void teo_reflect(struct cpuidle_device *dev, int state) { - struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu); + struct teo_cpu *cpu_data = this_cpu_ptr(&teo_cpus); + + cpu_data->tick_wakeup = tick_nohz_idle_got_tick(); 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; - } } /** @@ -508,13 +514,9 @@ 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; } |