tjh.dev
Linux kernel mirror (for testing)
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linux
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 int DAY_RESCALE = 288;
37static const unsigned int HOUR_RESCALE = 12;
38static const unsigned int FIVE_MINUTE_RESCALE = 1;
39static const unsigned int accounting_delay = (HZ * 300) / 22;
40static const unsigned int 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_miss_collisions);
50read_attribute(bypassed);
51
52SHOW(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
72STORE(bch_stats)
73{
74 return size;
75}
76
77static void bch_stats_release(struct kobject *k)
78{
79}
80
81static 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};
91static KTYPE(bch_stats);
92
93int 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
107void 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
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_miss_collisions);
145 scale_stat(&stats->sectors_bypassed);
146 }
147}
148
149static 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
182static 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
197void 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
206void 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
214void 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
221void 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}