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
SHOW(bch_stats)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
STORE(bch_stats)72 STORE(bch_stats)
73 {
74 return size;
75 }
76
bch_stats_release(struct kobject * k)77 static void bch_stats_release(struct kobject *k)
78 {
79 }
80
81 static struct attribute *bch_stats_attrs[] = {
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 ATTRIBUTE_GROUPS(bch_stats);
92 static KTYPE(bch_stats);
93
bch_cache_accounting_add_kobjs(struct cache_accounting * acc,struct kobject * parent)94 int bch_cache_accounting_add_kobjs(struct cache_accounting *acc,
95 struct kobject *parent)
96 {
97 int ret = kobject_add(&acc->total.kobj, parent,
98 "stats_total");
99 ret = ret ?: kobject_add(&acc->five_minute.kobj, parent,
100 "stats_five_minute");
101 ret = ret ?: kobject_add(&acc->hour.kobj, parent,
102 "stats_hour");
103 ret = ret ?: kobject_add(&acc->day.kobj, parent,
104 "stats_day");
105 return ret;
106 }
107
bch_cache_accounting_clear(struct cache_accounting * acc)108 void bch_cache_accounting_clear(struct cache_accounting *acc)
109 {
110 acc->total.cache_hits = 0;
111 acc->total.cache_misses = 0;
112 acc->total.cache_bypass_hits = 0;
113 acc->total.cache_bypass_misses = 0;
114 acc->total.cache_miss_collisions = 0;
115 acc->total.sectors_bypassed = 0;
116 }
117
bch_cache_accounting_destroy(struct cache_accounting * acc)118 void bch_cache_accounting_destroy(struct cache_accounting *acc)
119 {
120 kobject_put(&acc->total.kobj);
121 kobject_put(&acc->five_minute.kobj);
122 kobject_put(&acc->hour.kobj);
123 kobject_put(&acc->day.kobj);
124
125 atomic_set(&acc->closing, 1);
126 if (del_timer_sync(&acc->timer))
127 closure_return(&acc->cl);
128 }
129
130 /* EWMA scaling */
131
scale_stat(unsigned long * stat)132 static void scale_stat(unsigned long *stat)
133 {
134 *stat = ewma_add(*stat, 0, accounting_weight, 0);
135 }
136
scale_stats(struct cache_stats * stats,unsigned long rescale_at)137 static void scale_stats(struct cache_stats *stats, unsigned long rescale_at)
138 {
139 if (++stats->rescale == rescale_at) {
140 stats->rescale = 0;
141 scale_stat(&stats->cache_hits);
142 scale_stat(&stats->cache_misses);
143 scale_stat(&stats->cache_bypass_hits);
144 scale_stat(&stats->cache_bypass_misses);
145 scale_stat(&stats->cache_miss_collisions);
146 scale_stat(&stats->sectors_bypassed);
147 }
148 }
149
scale_accounting(struct timer_list * t)150 static void scale_accounting(struct timer_list *t)
151 {
152 struct cache_accounting *acc = from_timer(acc, t, timer);
153
154 #define move_stat(name) do { \
155 unsigned int 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_miss_collisions);
168 move_stat(sectors_bypassed);
169
170 scale_stats(&acc->total, 0);
171 scale_stats(&acc->day, DAY_RESCALE);
172 scale_stats(&acc->hour, HOUR_RESCALE);
173 scale_stats(&acc->five_minute, FIVE_MINUTE_RESCALE);
174
175 acc->timer.expires += accounting_delay;
176
177 if (!atomic_read(&acc->closing))
178 add_timer(&acc->timer);
179 else
180 closure_return(&acc->cl);
181 }
182
mark_cache_stats(struct cache_stat_collector * stats,bool hit,bool bypass)183 static void mark_cache_stats(struct cache_stat_collector *stats,
184 bool hit, bool bypass)
185 {
186 if (!bypass)
187 if (hit)
188 atomic_inc(&stats->cache_hits);
189 else
190 atomic_inc(&stats->cache_misses);
191 else
192 if (hit)
193 atomic_inc(&stats->cache_bypass_hits);
194 else
195 atomic_inc(&stats->cache_bypass_misses);
196 }
197
bch_mark_cache_accounting(struct cache_set * c,struct bcache_device * d,bool hit,bool bypass)198 void bch_mark_cache_accounting(struct cache_set *c, struct bcache_device *d,
199 bool hit, bool bypass)
200 {
201 struct cached_dev *dc = container_of(d, struct cached_dev, disk);
202
203 mark_cache_stats(&dc->accounting.collector, hit, bypass);
204 mark_cache_stats(&c->accounting.collector, hit, bypass);
205 }
206
bch_mark_cache_miss_collision(struct cache_set * c,struct bcache_device * d)207 void bch_mark_cache_miss_collision(struct cache_set *c, struct bcache_device *d)
208 {
209 struct cached_dev *dc = container_of(d, struct cached_dev, disk);
210
211 atomic_inc(&dc->accounting.collector.cache_miss_collisions);
212 atomic_inc(&c->accounting.collector.cache_miss_collisions);
213 }
214
bch_mark_sectors_bypassed(struct cache_set * c,struct cached_dev * dc,int sectors)215 void bch_mark_sectors_bypassed(struct cache_set *c, struct cached_dev *dc,
216 int sectors)
217 {
218 atomic_add(sectors, &dc->accounting.collector.sectors_bypassed);
219 atomic_add(sectors, &c->accounting.collector.sectors_bypassed);
220 }
221
bch_cache_accounting_init(struct cache_accounting * acc,struct closure * parent)222 void bch_cache_accounting_init(struct cache_accounting *acc,
223 struct closure *parent)
224 {
225 kobject_init(&acc->total.kobj, &bch_stats_ktype);
226 kobject_init(&acc->five_minute.kobj, &bch_stats_ktype);
227 kobject_init(&acc->hour.kobj, &bch_stats_ktype);
228 kobject_init(&acc->day.kobj, &bch_stats_ktype);
229
230 closure_init(&acc->cl, parent);
231 timer_setup(&acc->timer, scale_accounting, 0);
232 acc->timer.expires = jiffies + accounting_delay;
233 add_timer(&acc->timer);
234 }
235