tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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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_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(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_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
204 mark_cache_stats(&dc->accounting.collector, hit, bypass);
205 mark_cache_stats(&c->accounting.collector, hit, bypass);
206}
207
208void bch_mark_cache_readahead(struct cache_set *c, struct bcache_device *d)
209{
210 struct cached_dev *dc = container_of(d, struct cached_dev, disk);
211
212 atomic_inc(&dc->accounting.collector.cache_readaheads);
213 atomic_inc(&c->accounting.collector.cache_readaheads);
214}
215
216void bch_mark_cache_miss_collision(struct cache_set *c, struct bcache_device *d)
217{
218 struct cached_dev *dc = container_of(d, struct cached_dev, disk);
219
220 atomic_inc(&dc->accounting.collector.cache_miss_collisions);
221 atomic_inc(&c->accounting.collector.cache_miss_collisions);
222}
223
224void bch_mark_sectors_bypassed(struct cache_set *c, struct cached_dev *dc,
225 int sectors)
226{
227 atomic_add(sectors, &dc->accounting.collector.sectors_bypassed);
228 atomic_add(sectors, &c->accounting.collector.sectors_bypassed);
229}
230
231void bch_cache_accounting_init(struct cache_accounting *acc,
232 struct closure *parent)
233{
234 kobject_init(&acc->total.kobj, &bch_stats_ktype);
235 kobject_init(&acc->five_minute.kobj, &bch_stats_ktype);
236 kobject_init(&acc->hour.kobj, &bch_stats_ktype);
237 kobject_init(&acc->day.kobj, &bch_stats_ktype);
238
239 closure_init(&acc->cl, parent);
240 timer_setup(&acc->timer, scale_accounting, 0);
241 acc->timer.expires = jiffies + accounting_delay;
242 add_timer(&acc->timer);
243}