linux/drivers/md/bcache/stats.c
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   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
  36static const unsigned DAY_RESCALE               = 288;
  37static const unsigned HOUR_RESCALE              = 12;
  38static const unsigned FIVE_MINUTE_RESCALE       = 1;
  39static const unsigned accounting_delay          = (HZ * 300) / 22;
  40static const unsigned accounting_weight         = 32;
  41
  42/* sysfs reading/writing */
  43
  44read_attribute(cache_hits);
  45read_attribute(cache_misses);
  46read_attribute(cache_bypass_hits);
  47read_attribute(cache_bypass_misses);
  48read_attribute(cache_hit_ratio);
  49read_attribute(cache_readaheads);
  50read_attribute(cache_miss_collisions);
  51read_attribute(bypassed);
  52
  53SHOW(bch_stats)
  54{
  55        struct cache_stats *s =
  56                container_of(kobj, struct cache_stats, kobj);
  57#define var(stat)               (s->stat >> 16)
  58        var_print(cache_hits);
  59        var_print(cache_misses);
  60        var_print(cache_bypass_hits);
  61        var_print(cache_bypass_misses);
  62
  63        sysfs_print(cache_hit_ratio,
  64                    DIV_SAFE(var(cache_hits) * 100,
  65                             var(cache_hits) + var(cache_misses)));
  66
  67        var_print(cache_readaheads);
  68        var_print(cache_miss_collisions);
  69        sysfs_hprint(bypassed,  var(sectors_bypassed) << 9);
  70#undef var
  71        return 0;
  72}
  73
  74STORE(bch_stats)
  75{
  76        return size;
  77}
  78
  79static void bch_stats_release(struct kobject *k)
  80{
  81}
  82
  83static struct attribute *bch_stats_files[] = {
  84        &sysfs_cache_hits,
  85        &sysfs_cache_misses,
  86        &sysfs_cache_bypass_hits,
  87        &sysfs_cache_bypass_misses,
  88        &sysfs_cache_hit_ratio,
  89        &sysfs_cache_readaheads,
  90        &sysfs_cache_miss_collisions,
  91        &sysfs_bypassed,
  92        NULL
  93};
  94static KTYPE(bch_stats);
  95
  96int bch_cache_accounting_add_kobjs(struct cache_accounting *acc,
  97                                   struct kobject *parent)
  98{
  99        int ret = kobject_add(&acc->total.kobj, parent,
 100                              "stats_total");
 101        ret = ret ?: kobject_add(&acc->five_minute.kobj, parent,
 102                                 "stats_five_minute");
 103        ret = ret ?: kobject_add(&acc->hour.kobj, parent,
 104                                 "stats_hour");
 105        ret = ret ?: kobject_add(&acc->day.kobj, parent,
 106                                 "stats_day");
 107        return ret;
 108}
 109
 110void bch_cache_accounting_clear(struct cache_accounting *acc)
 111{
 112        memset(&acc->total.cache_hits,
 113               0,
 114               sizeof(unsigned long) * 7);
 115}
 116
 117void 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
 131static void scale_stat(unsigned long *stat)
 132{
 133        *stat =  ewma_add(*stat, 0, accounting_weight, 0);
 134}
 135
 136static 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_readaheads);
 145                scale_stat(&stats->cache_miss_collisions);
 146                scale_stat(&stats->sectors_bypassed);
 147        }
 148}
 149
 150static void scale_accounting(unsigned long data)
 151{
 152        struct cache_accounting *acc = (struct cache_accounting *) data;
 153
 154#define move_stat(name) do {                                            \
 155        unsigned t = atomic_xchg(&acc->collector.name, 0);              \
 156        t <<= 16;                                                       \
 157        acc->five_minute.name += t;                                     \
 158        acc->hour.name += t;                                            \
 159        acc->day.name += t;                                             \
 160        acc->total.name += t;                                           \
 161} while (0)
 162
 163        move_stat(cache_hits);
 164        move_stat(cache_misses);
 165        move_stat(cache_bypass_hits);
 166        move_stat(cache_bypass_misses);
 167        move_stat(cache_readaheads);
 168        move_stat(cache_miss_collisions);
 169        move_stat(sectors_bypassed);
 170
 171        scale_stats(&acc->total, 0);
 172        scale_stats(&acc->day, DAY_RESCALE);
 173        scale_stats(&acc->hour, HOUR_RESCALE);
 174        scale_stats(&acc->five_minute, FIVE_MINUTE_RESCALE);
 175
 176        acc->timer.expires += accounting_delay;
 177
 178        if (!atomic_read(&acc->closing))
 179                add_timer(&acc->timer);
 180        else
 181                closure_return(&acc->cl);
 182}
 183
 184static void mark_cache_stats(struct cache_stat_collector *stats,
 185                             bool hit, bool bypass)
 186{
 187        if (!bypass)
 188                if (hit)
 189                        atomic_inc(&stats->cache_hits);
 190                else
 191                        atomic_inc(&stats->cache_misses);
 192        else
 193                if (hit)
 194                        atomic_inc(&stats->cache_bypass_hits);
 195                else
 196                        atomic_inc(&stats->cache_bypass_misses);
 197}
 198
 199void bch_mark_cache_accounting(struct cache_set *c, struct bcache_device *d,
 200                               bool hit, bool bypass)
 201{
 202        struct cached_dev *dc = container_of(d, struct cached_dev, disk);
 203        mark_cache_stats(&dc->accounting.collector, hit, bypass);
 204        mark_cache_stats(&c->accounting.collector, hit, bypass);
 205}
 206
 207void bch_mark_cache_readahead(struct cache_set *c, struct bcache_device *d)
 208{
 209        struct cached_dev *dc = container_of(d, struct cached_dev, disk);
 210        atomic_inc(&dc->accounting.collector.cache_readaheads);
 211        atomic_inc(&c->accounting.collector.cache_readaheads);
 212}
 213
 214void bch_mark_cache_miss_collision(struct cache_set *c, struct bcache_device *d)
 215{
 216        struct cached_dev *dc = container_of(d, struct cached_dev, disk);
 217        atomic_inc(&dc->accounting.collector.cache_miss_collisions);
 218        atomic_inc(&c->accounting.collector.cache_miss_collisions);
 219}
 220
 221void bch_mark_sectors_bypassed(struct cache_set *c, struct cached_dev *dc,
 222                               int sectors)
 223{
 224        atomic_add(sectors, &dc->accounting.collector.sectors_bypassed);
 225        atomic_add(sectors, &c->accounting.collector.sectors_bypassed);
 226}
 227
 228void bch_cache_accounting_init(struct cache_accounting *acc,
 229                               struct closure *parent)
 230{
 231        kobject_init(&acc->total.kobj,          &bch_stats_ktype);
 232        kobject_init(&acc->five_minute.kobj,    &bch_stats_ktype);
 233        kobject_init(&acc->hour.kobj,           &bch_stats_ktype);
 234        kobject_init(&acc->day.kobj,            &bch_stats_ktype);
 235
 236        closure_init(&acc->cl, parent);
 237        init_timer(&acc->timer);
 238        acc->timer.expires      = jiffies + accounting_delay;
 239        acc->timer.data         = (unsigned long) acc;
 240        acc->timer.function     = scale_accounting;
 241        add_timer(&acc->timer);
 242}
 243