drivers/md/bcache/stats.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * bcache stats code
   4  *
   5  * Copyright 2012 Google, Inc.
   6  */
   7
   8 #include "bcache.h"
   9 #include "stats.h"
  10 #include "btree.h"
  11 #include "sysfs.h"
  12
  13 /*
  14  * We keep absolute totals of various statistics, and addionally a set of three
  15  * rolling averages.
  16  *
  17  * Every so often, a timer goes off and rescales the rolling averages.
  18  * accounting_rescale[] is how many times the timer has to go off before we
  19  * rescale each set of numbers; that gets us half lives of 5 minutes, one hour,
  20  * and one day.
  21  *
  22  * accounting_delay is how often the timer goes off - 22 times in 5 minutes,
  23  * and accounting_weight is what we use to rescale:
  24  *
  25  * pow(31 / 32, 22) ~= 1/2
  26  *
  27  * So that we don't have to increment each set of numbers every time we (say)
  28  * get a cache hit, we increment a single atomic_t in acc->collector, and when
  29  * the rescale function runs it resets the atomic counter to 0 and adds its
  30  * old value to each of the exported numbers.
  31  *
  32  * To reduce rounding error, the numbers in struct cache_stats are all
  33  * stored left shifted by 16, and scaled back in the sysfs show() function.
  34  */
  35
  36 static const unsigned int DAY_RESCALE           = 288;
  37 static const unsigned int HOUR_RESCALE          = 12;
  38 static const unsigned int FIVE_MINUTE_RESCALE   = 1;
  39 static const unsigned int accounting_delay      = (HZ * 300) / 22;
  40 static const unsigned int accounting_weight     = 32;
  41
  42 /* sysfs reading/writing */
  43
  44 read_attribute(cache_hits);
  45 read_attribute(cache_misses);
  46 read_attribute(cache_bypass_hits);
  47 read_attribute(cache_bypass_misses);
  48 read_attribute(cache_hit_ratio);
  49 read_attribute(cache_miss_collisions);
  50 read_attribute(bypassed);
  51
  52 SHOW(bch_stats)
  53 {
  54         struct cache_stats *s =
  55                 container_of(kobj, struct cache_stats, kobj);
  56 #define var(stat)               (s->stat >> 16)
  57         var_print(cache_hits);
  58         var_print(cache_misses);
  59         var_print(cache_bypass_hits);
  60         var_print(cache_bypass_misses);
  61
  62         sysfs_print(cache_hit_ratio,
  63                     DIV_SAFE(var(cache_hits) * 100,
  64                              var(cache_hits) + var(cache_misses)));
  65
  66         var_print(cache_miss_collisions);
  67         sysfs_hprint(bypassed,  var(sectors_bypassed) << 9);
  68 #undef var
  69         return 0;
  70 }
  71
  72 STORE(bch_stats)
  73 {
  74         return size;
  75 }
  76
  77 static void bch_stats_release(struct kobject *k)
  78 {
  79 }
  80
  81 static struct attribute *bch_stats_files[] = {
  82         &sysfs_cache_hits,
  83         &sysfs_cache_misses,
  84         &sysfs_cache_bypass_hits,
  85         &sysfs_cache_bypass_misses,
  86         &sysfs_cache_hit_ratio,
  87         &sysfs_cache_miss_collisions,
  88         &sysfs_bypassed,
  89         NULL
  90 };
  91 static KTYPE(bch_stats);
  92
  93 int bch_cache_accounting_add_kobjs(struct cache_accounting *acc,
  94                                    struct kobject *parent)
  95 {
  96         int ret = kobject_add(&acc->total.kobj, parent,
  97                               "stats_total");
  98         ret = ret ?: kobject_add(&acc->five_minute.kobj, parent,
  99                                  "stats_five_minute");
 100         ret = ret ?: kobject_add(&acc->hour.kobj, parent,
 101                                  "stats_hour");
 102         ret = ret ?: kobject_add(&acc->day.kobj, parent,
 103                                  "stats_day");
 104         return ret;
 105 }
 106
 107 void bch_cache_accounting_clear(struct cache_accounting *acc)
 108 {
 109         acc->total.cache_hits = 0;
 110         acc->total.cache_misses = 0;
 111         acc->total.cache_bypass_hits = 0;
 112         acc->total.cache_bypass_misses = 0;
 113         acc->total.cache_miss_collisions = 0;
 114         acc->total.sectors_bypassed = 0;
 115 }
 116
 117 void bch_cache_accounting_destroy(struct cache_accounting *acc)
 118 {
 119         kobject_put(&acc->total.kobj);
 120         kobject_put(&acc->five_minute.kobj);
 121         kobject_put(&acc->hour.kobj);
 122         kobject_put(&acc->day.kobj);
 123
 124         atomic_set(&acc->closing, 1);
 125         if (del_timer_sync(&acc->timer))
 126                 closure_return(&acc->cl);
 127 }
 128
 129 /* EWMA scaling */
 130
 131 static void scale_stat(unsigned long *stat)
 132 {
 133         *stat =  ewma_add(*stat, 0, accounting_weight, 0);
 134 }
 135
 136 static void scale_stats(struct cache_stats *stats, unsigned long rescale_at)
 137 {
 138         if (++stats->rescale == rescale_at) {
 139                 stats->rescale = 0;
 140                 scale_stat(&stats->cache_hits);
 141                 scale_stat(&stats->cache_misses);
 142                 scale_stat(&stats->cache_bypass_hits);
 143                 scale_stat(&stats->cache_bypass_misses);
 144                 scale_stat(&stats->cache_miss_collisions);
 145                 scale_stat(&stats->sectors_bypassed);
 146         }
 147 }
 148
 149 static void scale_accounting(struct timer_list *t)
 150 {
 151         struct cache_accounting *acc = from_timer(acc, t, timer);
 152
 153 #define move_stat(name) do {                                            \
 154         unsigned int t = atomic_xchg(&acc->collector.name, 0);          \
 155         t <<= 16;                                                       \
 156         acc->five_minute.name += t;                                     \
 157         acc->hour.name += t;                                            \
 158         acc->day.name += t;                                             \
 159         acc->total.name += t;                                           \
 160 } while (0)
 161
 162         move_stat(cache_hits);
 163         move_stat(cache_misses);
 164         move_stat(cache_bypass_hits);
 165         move_stat(cache_bypass_misses);
 166         move_stat(cache_miss_collisions);
 167         move_stat(sectors_bypassed);
 168
 169         scale_stats(&acc->total, 0);
 170         scale_stats(&acc->day, DAY_RESCALE);
 171         scale_stats(&acc->hour, HOUR_RESCALE);
 172         scale_stats(&acc->five_minute, FIVE_MINUTE_RESCALE);
 173
 174         acc->timer.expires += accounting_delay;
 175
 176         if (!atomic_read(&acc->closing))
 177                 add_timer(&acc->timer);
 178         else
 179                 closure_return(&acc->cl);
 180 }
 181
 182 static void mark_cache_stats(struct cache_stat_collector *stats,
 183                              bool hit, bool bypass)
 184 {
 185         if (!bypass)
 186                 if (hit)
 187                         atomic_inc(&stats->cache_hits);
 188                 else
 189                         atomic_inc(&stats->cache_misses);
 190         else
 191                 if (hit)
 192                         atomic_inc(&stats->cache_bypass_hits);
 193                 else
 194                         atomic_inc(&stats->cache_bypass_misses);
 195 }
 196
 197 void bch_mark_cache_accounting(struct cache_set *c, struct bcache_device *d,
 198                                bool hit, bool bypass)
 199 {
 200         struct cached_dev *dc = container_of(d, struct cached_dev, disk);
 201
 202         mark_cache_stats(&dc->accounting.collector, hit, bypass);
 203         mark_cache_stats(&c->accounting.collector, hit, bypass);
 204 }
 205
 206 void bch_mark_cache_miss_collision(struct cache_set *c, struct bcache_device *d)
 207 {
 208         struct cached_dev *dc = container_of(d, struct cached_dev, disk);
 209
 210         atomic_inc(&dc->accounting.collector.cache_miss_collisions);
 211         atomic_inc(&c->accounting.collector.cache_miss_collisions);
 212 }
 213
 214 void bch_mark_sectors_bypassed(struct cache_set *c, struct cached_dev *dc,
 215                                int sectors)
 216 {
 217         atomic_add(sectors, &dc->accounting.collector.sectors_bypassed);
 218         atomic_add(sectors, &c->accounting.collector.sectors_bypassed);
 219 }
 220
 221 void bch_cache_accounting_init(struct cache_accounting *acc,
 222                                struct closure *parent)
 223 {
 224         kobject_init(&acc->total.kobj,          &bch_stats_ktype);
 225         kobject_init(&acc->five_minute.kobj,    &bch_stats_ktype);
 226         kobject_init(&acc->hour.kobj,           &bch_stats_ktype);
 227         kobject_init(&acc->day.kobj,            &bch_stats_ktype);
 228
 229         closure_init(&acc->cl, parent);
 230         timer_setup(&acc->timer, scale_accounting, 0);
 231         acc->timer.expires      = jiffies + accounting_delay;
 232         add_timer(&acc->timer);
 233 }