LCOV - code coverage report
Current view: top level - drivers/cpuidle/governors - menu.c (source / functions) Hit Total Coverage
Test: combined.info Lines: 2 155 1.3 %
Date: 2022-04-01 14:58:12 Functions: 1 6 16.7 %
Branches: 0 118 0.0 %

           Branch data     Line data    Source code
       1                 :            : // SPDX-License-Identifier: GPL-2.0-only
       2                 :            : /*
       3                 :            :  * menu.c - the menu idle governor
       4                 :            :  *
       5                 :            :  * Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
       6                 :            :  * Copyright (C) 2009 Intel Corporation
       7                 :            :  * Author:
       8                 :            :  *        Arjan van de Ven <arjan@linux.intel.com>
       9                 :            :  */
      10                 :            : 
      11                 :            : #include <linux/kernel.h>
      12                 :            : #include <linux/cpuidle.h>
      13                 :            : #include <linux/time.h>
      14                 :            : #include <linux/ktime.h>
      15                 :            : #include <linux/hrtimer.h>
      16                 :            : #include <linux/tick.h>
      17                 :            : #include <linux/sched.h>
      18                 :            : #include <linux/sched/loadavg.h>
      19                 :            : #include <linux/sched/stat.h>
      20                 :            : #include <linux/math64.h>
      21                 :            : 
      22                 :            : #define BUCKETS 12
      23                 :            : #define INTERVAL_SHIFT 3
      24                 :            : #define INTERVALS (1UL << INTERVAL_SHIFT)
      25                 :            : #define RESOLUTION 1024
      26                 :            : #define DECAY 8
      27                 :            : #define MAX_INTERESTING (50000 * NSEC_PER_USEC)
      28                 :            : 
      29                 :            : /*
      30                 :            :  * Concepts and ideas behind the menu governor
      31                 :            :  *
      32                 :            :  * For the menu governor, there are 3 decision factors for picking a C
      33                 :            :  * state:
      34                 :            :  * 1) Energy break even point
      35                 :            :  * 2) Performance impact
      36                 :            :  * 3) Latency tolerance (from pmqos infrastructure)
      37                 :            :  * These these three factors are treated independently.
      38                 :            :  *
      39                 :            :  * Energy break even point
      40                 :            :  * -----------------------
      41                 :            :  * C state entry and exit have an energy cost, and a certain amount of time in
      42                 :            :  * the  C state is required to actually break even on this cost. CPUIDLE
      43                 :            :  * provides us this duration in the "target_residency" field. So all that we
      44                 :            :  * need is a good prediction of how long we'll be idle. Like the traditional
      45                 :            :  * menu governor, we start with the actual known "next timer event" time.
      46                 :            :  *
      47                 :            :  * Since there are other source of wakeups (interrupts for example) than
      48                 :            :  * the next timer event, this estimation is rather optimistic. To get a
      49                 :            :  * more realistic estimate, a correction factor is applied to the estimate,
      50                 :            :  * that is based on historic behavior. For example, if in the past the actual
      51                 :            :  * duration always was 50% of the next timer tick, the correction factor will
      52                 :            :  * be 0.5.
      53                 :            :  *
      54                 :            :  * menu uses a running average for this correction factor, however it uses a
      55                 :            :  * set of factors, not just a single factor. This stems from the realization
      56                 :            :  * that the ratio is dependent on the order of magnitude of the expected
      57                 :            :  * duration; if we expect 500 milliseconds of idle time the likelihood of
      58                 :            :  * getting an interrupt very early is much higher than if we expect 50 micro
      59                 :            :  * seconds of idle time. A second independent factor that has big impact on
      60                 :            :  * the actual factor is if there is (disk) IO outstanding or not.
      61                 :            :  * (as a special twist, we consider every sleep longer than 50 milliseconds
      62                 :            :  * as perfect; there are no power gains for sleeping longer than this)
      63                 :            :  *
      64                 :            :  * For these two reasons we keep an array of 12 independent factors, that gets
      65                 :            :  * indexed based on the magnitude of the expected duration as well as the
      66                 :            :  * "is IO outstanding" property.
      67                 :            :  *
      68                 :            :  * Repeatable-interval-detector
      69                 :            :  * ----------------------------
      70                 :            :  * There are some cases where "next timer" is a completely unusable predictor:
      71                 :            :  * Those cases where the interval is fixed, for example due to hardware
      72                 :            :  * interrupt mitigation, but also due to fixed transfer rate devices such as
      73                 :            :  * mice.
      74                 :            :  * For this, we use a different predictor: We track the duration of the last 8
      75                 :            :  * intervals and if the stand deviation of these 8 intervals is below a
      76                 :            :  * threshold value, we use the average of these intervals as prediction.
      77                 :            :  *
      78                 :            :  * Limiting Performance Impact
      79                 :            :  * ---------------------------
      80                 :            :  * C states, especially those with large exit latencies, can have a real
      81                 :            :  * noticeable impact on workloads, which is not acceptable for most sysadmins,
      82                 :            :  * and in addition, less performance has a power price of its own.
      83                 :            :  *
      84                 :            :  * As a general rule of thumb, menu assumes that the following heuristic
      85                 :            :  * holds:
      86                 :            :  *     The busier the system, the less impact of C states is acceptable
      87                 :            :  *
      88                 :            :  * This rule-of-thumb is implemented using a performance-multiplier:
      89                 :            :  * If the exit latency times the performance multiplier is longer than
      90                 :            :  * the predicted duration, the C state is not considered a candidate
      91                 :            :  * for selection due to a too high performance impact. So the higher
      92                 :            :  * this multiplier is, the longer we need to be idle to pick a deep C
      93                 :            :  * state, and thus the less likely a busy CPU will hit such a deep
      94                 :            :  * C state.
      95                 :            :  *
      96                 :            :  * Two factors are used in determing this multiplier:
      97                 :            :  * a value of 10 is added for each point of "per cpu load average" we have.
      98                 :            :  * a value of 5 points is added for each process that is waiting for
      99                 :            :  * IO on this CPU.
     100                 :            :  * (these values are experimentally determined)
     101                 :            :  *
     102                 :            :  * The load average factor gives a longer term (few seconds) input to the
     103                 :            :  * decision, while the iowait value gives a cpu local instantanious input.
     104                 :            :  * The iowait factor may look low, but realize that this is also already
     105                 :            :  * represented in the system load average.
     106                 :            :  *
     107                 :            :  */
     108                 :            : 
     109                 :            : struct menu_device {
     110                 :            :         int             needs_update;
     111                 :            :         int             tick_wakeup;
     112                 :            : 
     113                 :            :         u64             next_timer_ns;
     114                 :            :         unsigned int    bucket;
     115                 :            :         unsigned int    correction_factor[BUCKETS];
     116                 :            :         unsigned int    intervals[INTERVALS];
     117                 :            :         int             interval_ptr;
     118                 :            : };
     119                 :            : 
     120                 :          0 : static inline int which_bucket(u64 duration_ns, unsigned long nr_iowaiters)
     121                 :            : {
     122                 :          0 :         int bucket = 0;
     123                 :            : 
     124                 :            :         /*
     125                 :            :          * We keep two groups of stats; one with no
     126                 :            :          * IO pending, one without.
     127                 :            :          * This allows us to calculate
     128                 :            :          * E(duration)|iowait
     129                 :            :          */
     130                 :          0 :         if (nr_iowaiters)
     131                 :          0 :                 bucket = BUCKETS/2;
     132                 :            : 
     133         [ #  # ]:          0 :         if (duration_ns < 10ULL * NSEC_PER_USEC)
     134                 :            :                 return bucket;
     135         [ #  # ]:          0 :         if (duration_ns < 100ULL * NSEC_PER_USEC)
     136                 :          0 :                 return bucket + 1;
     137         [ #  # ]:          0 :         if (duration_ns < 1000ULL * NSEC_PER_USEC)
     138                 :          0 :                 return bucket + 2;
     139         [ #  # ]:          0 :         if (duration_ns < 10000ULL * NSEC_PER_USEC)
     140                 :          0 :                 return bucket + 3;
     141         [ #  # ]:          0 :         if (duration_ns < 100000ULL * NSEC_PER_USEC)
     142                 :          0 :                 return bucket + 4;
     143                 :          0 :         return bucket + 5;
     144                 :            : }
     145                 :            : 
     146                 :            : /*
     147                 :            :  * Return a multiplier for the exit latency that is intended
     148                 :            :  * to take performance requirements into account.
     149                 :            :  * The more performance critical we estimate the system
     150                 :            :  * to be, the higher this multiplier, and thus the higher
     151                 :            :  * the barrier to go to an expensive C state.
     152                 :            :  */
     153                 :          0 : static inline int performance_multiplier(unsigned long nr_iowaiters)
     154                 :            : {
     155                 :            :         /* for IO wait tasks (per cpu!) we add 10x each */
     156                 :          0 :         return 1 + 10 * nr_iowaiters;
     157                 :            : }
     158                 :            : 
     159                 :            : static DEFINE_PER_CPU(struct menu_device, menu_devices);
     160                 :            : 
     161                 :            : static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev);
     162                 :            : 
     163                 :            : /*
     164                 :            :  * Try detecting repeating patterns by keeping track of the last 8
     165                 :            :  * intervals, and checking if the standard deviation of that set
     166                 :            :  * of points is below a threshold. If it is... then use the
     167                 :            :  * average of these 8 points as the estimated value.
     168                 :            :  */
     169                 :          0 : static unsigned int get_typical_interval(struct menu_device *data,
     170                 :            :                                          unsigned int predicted_us)
     171                 :            : {
     172                 :          0 :         int i, divisor;
     173                 :          0 :         unsigned int min, max, thresh, avg;
     174                 :          0 :         uint64_t sum, variance;
     175                 :            : 
     176                 :          0 :         thresh = INT_MAX; /* Discard outliers above this value */
     177                 :            : 
     178                 :          0 : again:
     179                 :            : 
     180                 :            :         /* First calculate the average of past intervals */
     181                 :          0 :         min = UINT_MAX;
     182                 :          0 :         max = 0;
     183                 :          0 :         sum = 0;
     184                 :          0 :         divisor = 0;
     185         [ #  # ]:          0 :         for (i = 0; i < INTERVALS; i++) {
     186                 :          0 :                 unsigned int value = data->intervals[i];
     187         [ #  # ]:          0 :                 if (value <= thresh) {
     188                 :          0 :                         sum += value;
     189                 :          0 :                         divisor++;
     190                 :          0 :                         if (value > max)
     191                 :            :                                 max = value;
     192                 :            : 
     193                 :          0 :                         if (value < min)
     194                 :            :                                 min = value;
     195                 :            :                 }
     196                 :            :         }
     197                 :            : 
     198                 :            :         /*
     199                 :            :          * If the result of the computation is going to be discarded anyway,
     200                 :            :          * avoid the computation altogether.
     201                 :            :          */
     202         [ #  # ]:          0 :         if (min >= predicted_us)
     203                 :            :                 return UINT_MAX;
     204                 :            : 
     205         [ #  # ]:          0 :         if (divisor == INTERVALS)
     206                 :          0 :                 avg = sum >> INTERVAL_SHIFT;
     207                 :            :         else
     208                 :          0 :                 avg = div_u64(sum, divisor);
     209                 :            : 
     210                 :            :         /* Then try to determine variance */
     211                 :          0 :         variance = 0;
     212         [ #  # ]:          0 :         for (i = 0; i < INTERVALS; i++) {
     213                 :          0 :                 unsigned int value = data->intervals[i];
     214         [ #  # ]:          0 :                 if (value <= thresh) {
     215                 :          0 :                         int64_t diff = (int64_t)value - avg;
     216                 :          0 :                         variance += diff * diff;
     217                 :            :                 }
     218                 :            :         }
     219         [ #  # ]:          0 :         if (divisor == INTERVALS)
     220                 :          0 :                 variance >>= INTERVAL_SHIFT;
     221                 :            :         else
     222                 :          0 :                 do_div(variance, divisor);
     223                 :            : 
     224                 :            :         /*
     225                 :            :          * The typical interval is obtained when standard deviation is
     226                 :            :          * small (stddev <= 20 us, variance <= 400 us^2) or standard
     227                 :            :          * deviation is small compared to the average interval (avg >
     228                 :            :          * 6*stddev, avg^2 > 36*variance). The average is smaller than
     229                 :            :          * UINT_MAX aka U32_MAX, so computing its square does not
     230                 :            :          * overflow a u64. We simply reject this candidate average if
     231                 :            :          * the standard deviation is greater than 715 s (which is
     232                 :            :          * rather unlikely).
     233                 :            :          *
     234                 :            :          * Use this result only if there is no timer to wake us up sooner.
     235                 :            :          */
     236         [ #  # ]:          0 :         if (likely(variance <= U64_MAX/36)) {
     237   [ #  #  #  # ]:          0 :                 if ((((u64)avg*avg > variance*36) && (divisor * 4 >= INTERVALS * 3))
     238         [ #  # ]:          0 :                                                         || variance <= 400) {
     239                 :          0 :                         return avg;
     240                 :            :                 }
     241                 :            :         }
     242                 :            : 
     243                 :            :         /*
     244                 :            :          * If we have outliers to the upside in our distribution, discard
     245                 :            :          * those by setting the threshold to exclude these outliers, then
     246                 :            :          * calculate the average and standard deviation again. Once we get
     247                 :            :          * down to the bottom 3/4 of our samples, stop excluding samples.
     248                 :            :          *
     249                 :            :          * This can deal with workloads that have long pauses interspersed
     250                 :            :          * with sporadic activity with a bunch of short pauses.
     251                 :            :          */
     252         [ #  # ]:          0 :         if ((divisor * 4) <= INTERVALS * 3)
     253                 :            :                 return UINT_MAX;
     254                 :            : 
     255                 :          0 :         thresh = max - 1;
     256                 :          0 :         goto again;
     257                 :            : }
     258                 :            : 
     259                 :            : /**
     260                 :            :  * menu_select - selects the next idle state to enter
     261                 :            :  * @drv: cpuidle driver containing state data
     262                 :            :  * @dev: the CPU
     263                 :            :  * @stop_tick: indication on whether or not to stop the tick
     264                 :            :  */
     265                 :          0 : static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
     266                 :            :                        bool *stop_tick)
     267                 :            : {
     268                 :          0 :         struct menu_device *data = this_cpu_ptr(&menu_devices);
     269                 :          0 :         s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
     270                 :          0 :         unsigned int predicted_us;
     271                 :          0 :         u64 predicted_ns;
     272                 :          0 :         u64 interactivity_req;
     273                 :          0 :         unsigned long nr_iowaiters;
     274                 :          0 :         ktime_t delta_next;
     275                 :          0 :         int i, idx;
     276                 :            : 
     277         [ #  # ]:          0 :         if (data->needs_update) {
     278                 :          0 :                 menu_update(drv, dev);
     279                 :          0 :                 data->needs_update = 0;
     280                 :            :         }
     281                 :            : 
     282                 :            :         /* determine the expected residency time, round up */
     283                 :          0 :         data->next_timer_ns = tick_nohz_get_sleep_length(&delta_next);
     284                 :            : 
     285                 :          0 :         nr_iowaiters = nr_iowait_cpu(dev->cpu);
     286         [ #  # ]:          0 :         data->bucket = which_bucket(data->next_timer_ns, nr_iowaiters);
     287                 :            : 
     288   [ #  #  #  # ]:          0 :         if (unlikely(drv->state_count <= 1 || latency_req == 0) ||
     289         [ #  # ]:          0 :             ((data->next_timer_ns < drv->states[1].target_residency_ns ||
     290         [ #  # ]:          0 :               latency_req < drv->states[1].exit_latency_ns) &&
     291         [ #  # ]:          0 :              !dev->states_usage[0].disable)) {
     292                 :            :                 /*
     293                 :            :                  * In this case state[0] will be used no matter what, so return
     294                 :            :                  * it right away and keep the tick running if state[0] is a
     295                 :            :                  * polling one.
     296                 :            :                  */
     297                 :          0 :                 *stop_tick = !(drv->states[0].flags & CPUIDLE_FLAG_POLLING);
     298                 :          0 :                 return 0;
     299                 :            :         }
     300                 :            : 
     301                 :            :         /* Round up the result for half microseconds. */
     302                 :          0 :         predicted_us = div_u64(data->next_timer_ns *
     303                 :          0 :                                data->correction_factor[data->bucket] +
     304                 :            :                                (RESOLUTION * DECAY * NSEC_PER_USEC) / 2,
     305                 :            :                                RESOLUTION * DECAY * NSEC_PER_USEC);
     306                 :            :         /* Use the lowest expected idle interval to pick the idle state. */
     307                 :          0 :         predicted_ns = (u64)min(predicted_us,
     308                 :            :                                 get_typical_interval(data, predicted_us)) *
     309                 :            :                                 NSEC_PER_USEC;
     310                 :            : 
     311         [ #  # ]:          0 :         if (tick_nohz_tick_stopped()) {
     312                 :            :                 /*
     313                 :            :                  * If the tick is already stopped, the cost of possible short
     314                 :            :                  * idle duration misprediction is much higher, because the CPU
     315                 :            :                  * may be stuck in a shallow idle state for a long time as a
     316                 :            :                  * result of it.  In that case say we might mispredict and use
     317                 :            :                  * the known time till the closest timer event for the idle
     318                 :            :                  * state selection.
     319                 :            :                  */
     320         [ #  # ]:          0 :                 if (predicted_ns < TICK_NSEC)
     321                 :          0 :                         predicted_ns = delta_next;
     322                 :            :         } else {
     323                 :            :                 /*
     324                 :            :                  * Use the performance multiplier and the user-configurable
     325                 :            :                  * latency_req to determine the maximum exit latency.
     326                 :            :                  */
     327         [ #  # ]:          0 :                 interactivity_req = div64_u64(predicted_ns,
     328                 :            :                                               performance_multiplier(nr_iowaiters));
     329         [ #  # ]:          0 :                 if (latency_req > interactivity_req)
     330                 :          0 :                         latency_req = interactivity_req;
     331                 :            :         }
     332                 :            : 
     333                 :            :         /*
     334                 :            :          * Find the idle state with the lowest power while satisfying
     335                 :            :          * our constraints.
     336                 :            :          */
     337                 :          0 :         idx = -1;
     338         [ #  # ]:          0 :         for (i = 0; i < drv->state_count; i++) {
     339                 :          0 :                 struct cpuidle_state *s = &drv->states[i];
     340                 :            : 
     341         [ #  # ]:          0 :                 if (dev->states_usage[i].disable)
     342                 :          0 :                         continue;
     343                 :            : 
     344         [ #  # ]:          0 :                 if (idx == -1)
     345                 :          0 :                         idx = i; /* first enabled state */
     346                 :            : 
     347         [ #  # ]:          0 :                 if (s->target_residency_ns > predicted_ns) {
     348                 :            :                         /*
     349                 :            :                          * Use a physical idle state, not busy polling, unless
     350                 :            :                          * a timer is going to trigger soon enough.
     351                 :            :                          */
     352         [ #  # ]:          0 :                         if ((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) &&
     353         [ #  # ]:          0 :                             s->exit_latency_ns <= latency_req &&
     354         [ #  # ]:          0 :                             s->target_residency_ns <= data->next_timer_ns) {
     355                 :            :                                 predicted_ns = s->target_residency_ns;
     356                 :            :                                 idx = i;
     357                 :            :                                 break;
     358                 :            :                         }
     359         [ #  # ]:          0 :                         if (predicted_ns < TICK_NSEC)
     360                 :            :                                 break;
     361                 :            : 
     362         [ #  # ]:          0 :                         if (!tick_nohz_tick_stopped()) {
     363                 :            :                                 /*
     364                 :            :                                  * If the state selected so far is shallow,
     365                 :            :                                  * waking up early won't hurt, so retain the
     366                 :            :                                  * tick in that case and let the governor run
     367                 :            :                                  * again in the next iteration of the loop.
     368                 :            :                                  */
     369                 :          0 :                                 predicted_ns = drv->states[idx].target_residency_ns;
     370                 :          0 :                                 break;
     371                 :            :                         }
     372                 :            : 
     373                 :            :                         /*
     374                 :            :                          * If the state selected so far is shallow and this
     375                 :            :                          * state's target residency matches the time till the
     376                 :            :                          * closest timer event, select this one to avoid getting
     377                 :            :                          * stuck in the shallow one for too long.
     378                 :            :                          */
     379         [ #  # ]:          0 :                         if (drv->states[idx].target_residency_ns < TICK_NSEC &&
     380         [ #  # ]:          0 :                             s->target_residency_ns <= delta_next)
     381                 :          0 :                                 idx = i;
     382                 :            : 
     383                 :          0 :                         return idx;
     384                 :            :                 }
     385         [ #  # ]:          0 :                 if (s->exit_latency_ns > latency_req)
     386                 :            :                         break;
     387                 :            : 
     388                 :            :                 idx = i;
     389                 :            :         }
     390                 :            : 
     391         [ #  # ]:          0 :         if (idx == -1)
     392                 :          0 :                 idx = 0; /* No states enabled. Must use 0. */
     393                 :            : 
     394                 :            :         /*
     395                 :            :          * Don't stop the tick if the selected state is a polling one or if the
     396                 :            :          * expected idle duration is shorter than the tick period length.
     397                 :            :          */
     398   [ #  #  #  # ]:          0 :         if (((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
     399         [ #  # ]:          0 :              predicted_ns < TICK_NSEC) && !tick_nohz_tick_stopped()) {
     400                 :          0 :                 *stop_tick = false;
     401                 :            : 
     402   [ #  #  #  # ]:          0 :                 if (idx > 0 && drv->states[idx].target_residency_ns > delta_next) {
     403                 :            :                         /*
     404                 :            :                          * The tick is not going to be stopped and the target
     405                 :            :                          * residency of the state to be returned is not within
     406                 :            :                          * the time until the next timer event including the
     407                 :            :                          * tick, so try to correct that.
     408                 :            :                          */
     409         [ #  # ]:          0 :                         for (i = idx - 1; i >= 0; i--) {
     410         [ #  # ]:          0 :                                 if (dev->states_usage[i].disable)
     411                 :          0 :                                         continue;
     412                 :            : 
     413                 :          0 :                                 idx = i;
     414         [ #  # ]:          0 :                                 if (drv->states[i].target_residency_ns <= delta_next)
     415                 :            :                                         break;
     416                 :            :                         }
     417                 :            :                 }
     418                 :            :         }
     419                 :            : 
     420                 :            :         return idx;
     421                 :            : }
     422                 :            : 
     423                 :            : /**
     424                 :            :  * menu_reflect - records that data structures need update
     425                 :            :  * @dev: the CPU
     426                 :            :  * @index: the index of actual entered state
     427                 :            :  *
     428                 :            :  * NOTE: it's important to be fast here because this operation will add to
     429                 :            :  *       the overall exit latency.
     430                 :            :  */
     431                 :          0 : static void menu_reflect(struct cpuidle_device *dev, int index)
     432                 :            : {
     433                 :          0 :         struct menu_device *data = this_cpu_ptr(&menu_devices);
     434                 :            : 
     435                 :          0 :         dev->last_state_idx = index;
     436                 :          0 :         data->needs_update = 1;
     437                 :          0 :         data->tick_wakeup = tick_nohz_idle_got_tick();
     438                 :          0 : }
     439                 :            : 
     440                 :            : /**
     441                 :            :  * menu_update - attempts to guess what happened after entry
     442                 :            :  * @drv: cpuidle driver containing state data
     443                 :            :  * @dev: the CPU
     444                 :            :  */
     445                 :          0 : static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
     446                 :            : {
     447                 :          0 :         struct menu_device *data = this_cpu_ptr(&menu_devices);
     448                 :          0 :         int last_idx = dev->last_state_idx;
     449                 :          0 :         struct cpuidle_state *target = &drv->states[last_idx];
     450                 :          0 :         u64 measured_ns;
     451                 :          0 :         unsigned int new_factor;
     452                 :            : 
     453                 :            :         /*
     454                 :            :          * Try to figure out how much time passed between entry to low
     455                 :            :          * power state and occurrence of the wakeup event.
     456                 :            :          *
     457                 :            :          * If the entered idle state didn't support residency measurements,
     458                 :            :          * we use them anyway if they are short, and if long,
     459                 :            :          * truncate to the whole expected time.
     460                 :            :          *
     461                 :            :          * Any measured amount of time will include the exit latency.
     462                 :            :          * Since we are interested in when the wakeup begun, not when it
     463                 :            :          * was completed, we must subtract the exit latency. However, if
     464                 :            :          * the measured amount of time is less than the exit latency,
     465                 :            :          * assume the state was never reached and the exit latency is 0.
     466                 :            :          */
     467                 :            : 
     468   [ #  #  #  # ]:          0 :         if (data->tick_wakeup && data->next_timer_ns > TICK_NSEC) {
     469                 :            :                 /*
     470                 :            :                  * The nohz code said that there wouldn't be any events within
     471                 :            :                  * the tick boundary (if the tick was stopped), but the idle
     472                 :            :                  * duration predictor had a differing opinion.  Since the CPU
     473                 :            :                  * was woken up by a tick (that wasn't stopped after all), the
     474                 :            :                  * predictor was not quite right, so assume that the CPU could
     475                 :            :                  * have been idle long (but not forever) to help the idle
     476                 :            :                  * duration predictor do a better job next time.
     477                 :            :                  */
     478                 :            :                 measured_ns = 9 * MAX_INTERESTING / 10;
     479   [ #  #  #  # ]:          0 :         } else if ((drv->states[last_idx].flags & CPUIDLE_FLAG_POLLING) &&
     480                 :            :                    dev->poll_time_limit) {
     481                 :            :                 /*
     482                 :            :                  * The CPU exited the "polling" state due to a time limit, so
     483                 :            :                  * the idle duration prediction leading to the selection of that
     484                 :            :                  * state was inaccurate.  If a better prediction had been made,
     485                 :            :                  * the CPU might have been woken up from idle by the next timer.
     486                 :            :                  * Assume that to be the case.
     487                 :            :                  */
     488                 :          0 :                 measured_ns = data->next_timer_ns;
     489                 :            :         } else {
     490                 :            :                 /* measured value */
     491                 :          0 :                 measured_ns = dev->last_residency_ns;
     492                 :            : 
     493                 :            :                 /* Deduct exit latency */
     494         [ #  # ]:          0 :                 if (measured_ns > 2 * target->exit_latency_ns)
     495                 :          0 :                         measured_ns -= target->exit_latency_ns;
     496                 :            :                 else
     497                 :          0 :                         measured_ns /= 2;
     498                 :            :         }
     499                 :            : 
     500                 :            :         /* Make sure our coefficients do not exceed unity */
     501                 :          0 :         if (measured_ns > data->next_timer_ns)
     502                 :            :                 measured_ns = data->next_timer_ns;
     503                 :            : 
     504                 :            :         /* Update our correction ratio */
     505                 :          0 :         new_factor = data->correction_factor[data->bucket];
     506                 :          0 :         new_factor -= new_factor / DECAY;
     507                 :            : 
     508   [ #  #  #  # ]:          0 :         if (data->next_timer_ns > 0 && measured_ns < MAX_INTERESTING)
     509                 :          0 :                 new_factor += div64_u64(RESOLUTION * measured_ns,
     510                 :          0 :                                         data->next_timer_ns);
     511                 :            :         else
     512                 :            :                 /*
     513                 :            :                  * we were idle so long that we count it as a perfect
     514                 :            :                  * prediction
     515                 :            :                  */
     516                 :          0 :                 new_factor += RESOLUTION;
     517                 :            : 
     518                 :            :         /*
     519                 :            :          * We don't want 0 as factor; we always want at least
     520                 :            :          * a tiny bit of estimated time. Fortunately, due to rounding,
     521                 :            :          * new_factor will stay nonzero regardless of measured_us values
     522                 :            :          * and the compiler can eliminate this test as long as DECAY > 1.
     523                 :            :          */
     524                 :          0 :         if (DECAY == 1 && unlikely(new_factor == 0))
     525                 :            :                 new_factor = 1;
     526                 :            : 
     527                 :          0 :         data->correction_factor[data->bucket] = new_factor;
     528                 :            : 
     529                 :            :         /* update the repeating-pattern data */
     530         [ #  # ]:          0 :         data->intervals[data->interval_ptr++] = ktime_to_us(measured_ns);
     531         [ #  # ]:          0 :         if (data->interval_ptr >= INTERVALS)
     532                 :          0 :                 data->interval_ptr = 0;
     533                 :          0 : }
     534                 :            : 
     535                 :            : /**
     536                 :            :  * menu_enable_device - scans a CPU's states and does setup
     537                 :            :  * @drv: cpuidle driver
     538                 :            :  * @dev: the CPU
     539                 :            :  */
     540                 :          0 : static int menu_enable_device(struct cpuidle_driver *drv,
     541                 :            :                                 struct cpuidle_device *dev)
     542                 :            : {
     543                 :          0 :         struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
     544                 :          0 :         int i;
     545                 :            : 
     546                 :          0 :         memset(data, 0, sizeof(struct menu_device));
     547                 :            : 
     548                 :            :         /*
     549                 :            :          * if the correction factor is 0 (eg first time init or cpu hotplug
     550                 :            :          * etc), we actually want to start out with a unity factor.
     551                 :            :          */
     552         [ #  # ]:          0 :         for(i = 0; i < BUCKETS; i++)
     553                 :          0 :                 data->correction_factor[i] = RESOLUTION * DECAY;
     554                 :            : 
     555                 :          0 :         return 0;
     556                 :            : }
     557                 :            : 
     558                 :            : static struct cpuidle_governor menu_governor = {
     559                 :            :         .name =         "menu",
     560                 :            :         .rating =       20,
     561                 :            :         .enable =       menu_enable_device,
     562                 :            :         .select =       menu_select,
     563                 :            :         .reflect =      menu_reflect,
     564                 :            : };
     565                 :            : 
     566                 :            : /**
     567                 :            :  * init_menu - initializes the governor
     568                 :            :  */
     569                 :          3 : static int __init init_menu(void)
     570                 :            : {
     571                 :          3 :         return cpuidle_register_governor(&menu_governor);
     572                 :            : }
     573                 :            : 
     574                 :            : postcore_initcall(init_menu);

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