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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
f3109a51 JK |
2 | /* |
3 | * Floating proportions with flexible aging period | |
4 | * | |
5 | * Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz> | |
6 | * | |
7 | * The goal of this code is: Given different types of event, measure proportion | |
8 | * of each type of event over time. The proportions are measured with | |
9 | * exponentially decaying history to give smooth transitions. A formula | |
10 | * expressing proportion of event of type 'j' is: | |
11 | * | |
12 | * p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1}) | |
13 | * | |
14 | * Where x_{i,j} is j's number of events in i-th last time period and x_i is | |
15 | * total number of events in i-th last time period. | |
16 | * | |
17 | * Note that p_{j}'s are normalised, i.e. | |
18 | * | |
19 | * \Sum_{j} p_{j} = 1, | |
20 | * | |
bdb428c8 | 21 | * This formula can be straightforwardly computed by maintaining denominator |
f3109a51 JK |
22 | * (let's call it 'd') and for each event type its numerator (let's call it |
23 | * 'n_j'). When an event of type 'j' happens, we simply need to do: | |
24 | * n_j++; d++; | |
25 | * | |
26 | * When a new period is declared, we could do: | |
27 | * d /= 2 | |
28 | * for each j | |
29 | * n_j /= 2 | |
30 | * | |
31 | * To avoid iteration over all event types, we instead shift numerator of event | |
32 | * j lazily when someone asks for a proportion of event j or when event j | |
33 | * occurs. This can bit trivially implemented by remembering last period in | |
34 | * which something happened with proportion of type j. | |
35 | */ | |
36 | #include <linux/flex_proportions.h> | |
37 | ||
20ae0079 | 38 | int fprop_global_init(struct fprop_global *p, gfp_t gfp) |
f3109a51 JK |
39 | { |
40 | int err; | |
41 | ||
42 | p->period = 0; | |
43 | /* Use 1 to avoid dealing with periods with 0 events... */ | |
20ae0079 | 44 | err = percpu_counter_init(&p->events, 1, gfp); |
f3109a51 JK |
45 | if (err) |
46 | return err; | |
47 | seqcount_init(&p->sequence); | |
48 | return 0; | |
49 | } | |
50 | ||
51 | void fprop_global_destroy(struct fprop_global *p) | |
52 | { | |
53 | percpu_counter_destroy(&p->events); | |
54 | } | |
55 | ||
56 | /* | |
57 | * Declare @periods new periods. It is upto the caller to make sure period | |
58 | * transitions cannot happen in parallel. | |
59 | * | |
60 | * The function returns true if the proportions are still defined and false | |
61 | * if aging zeroed out all events. This can be used to detect whether declaring | |
62 | * further periods has any effect. | |
63 | */ | |
64 | bool fprop_new_period(struct fprop_global *p, int periods) | |
65 | { | |
a91befde | 66 | s64 events = percpu_counter_sum(&p->events); |
f3109a51 JK |
67 | |
68 | /* | |
69 | * Don't do anything if there are no events. | |
70 | */ | |
a91befde | 71 | if (events <= 1) |
f3109a51 JK |
72 | return false; |
73 | write_seqcount_begin(&p->sequence); | |
74 | if (periods < 64) | |
75 | events -= events >> periods; | |
76 | /* Use addition to avoid losing events happening between sum and set */ | |
77 | percpu_counter_add(&p->events, -events); | |
78 | p->period += periods; | |
79 | write_seqcount_end(&p->sequence); | |
80 | ||
81 | return true; | |
82 | } | |
83 | ||
84 | /* | |
85 | * ---- SINGLE ---- | |
86 | */ | |
87 | ||
88 | int fprop_local_init_single(struct fprop_local_single *pl) | |
89 | { | |
90 | pl->events = 0; | |
91 | pl->period = 0; | |
92 | raw_spin_lock_init(&pl->lock); | |
93 | return 0; | |
94 | } | |
95 | ||
96 | void fprop_local_destroy_single(struct fprop_local_single *pl) | |
97 | { | |
98 | } | |
99 | ||
100 | static void fprop_reflect_period_single(struct fprop_global *p, | |
101 | struct fprop_local_single *pl) | |
102 | { | |
103 | unsigned int period = p->period; | |
104 | unsigned long flags; | |
105 | ||
106 | /* Fast path - period didn't change */ | |
107 | if (pl->period == period) | |
108 | return; | |
109 | raw_spin_lock_irqsave(&pl->lock, flags); | |
110 | /* Someone updated pl->period while we were spinning? */ | |
111 | if (pl->period >= period) { | |
112 | raw_spin_unlock_irqrestore(&pl->lock, flags); | |
113 | return; | |
114 | } | |
115 | /* Aging zeroed our fraction? */ | |
116 | if (period - pl->period < BITS_PER_LONG) | |
117 | pl->events >>= period - pl->period; | |
118 | else | |
119 | pl->events = 0; | |
120 | pl->period = period; | |
121 | raw_spin_unlock_irqrestore(&pl->lock, flags); | |
122 | } | |
123 | ||
124 | /* Event of type pl happened */ | |
125 | void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl) | |
126 | { | |
127 | fprop_reflect_period_single(p, pl); | |
128 | pl->events++; | |
129 | percpu_counter_add(&p->events, 1); | |
130 | } | |
131 | ||
132 | /* Return fraction of events of type pl */ | |
133 | void fprop_fraction_single(struct fprop_global *p, | |
134 | struct fprop_local_single *pl, | |
135 | unsigned long *numerator, unsigned long *denominator) | |
136 | { | |
137 | unsigned int seq; | |
138 | s64 num, den; | |
139 | ||
140 | do { | |
141 | seq = read_seqcount_begin(&p->sequence); | |
142 | fprop_reflect_period_single(p, pl); | |
143 | num = pl->events; | |
144 | den = percpu_counter_read_positive(&p->events); | |
145 | } while (read_seqcount_retry(&p->sequence, seq)); | |
146 | ||
147 | /* | |
148 | * Make fraction <= 1 and denominator > 0 even in presence of percpu | |
149 | * counter errors | |
150 | */ | |
151 | if (den <= num) { | |
152 | if (num) | |
153 | den = num; | |
154 | else | |
155 | den = 1; | |
156 | } | |
157 | *denominator = den; | |
158 | *numerator = num; | |
159 | } | |
160 | ||
161 | /* | |
162 | * ---- PERCPU ---- | |
163 | */ | |
164 | #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids))) | |
165 | ||
20ae0079 | 166 | int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp) |
f3109a51 JK |
167 | { |
168 | int err; | |
169 | ||
20ae0079 | 170 | err = percpu_counter_init(&pl->events, 0, gfp); |
f3109a51 JK |
171 | if (err) |
172 | return err; | |
173 | pl->period = 0; | |
174 | raw_spin_lock_init(&pl->lock); | |
175 | return 0; | |
176 | } | |
177 | ||
178 | void fprop_local_destroy_percpu(struct fprop_local_percpu *pl) | |
179 | { | |
180 | percpu_counter_destroy(&pl->events); | |
181 | } | |
182 | ||
183 | static void fprop_reflect_period_percpu(struct fprop_global *p, | |
184 | struct fprop_local_percpu *pl) | |
185 | { | |
186 | unsigned int period = p->period; | |
187 | unsigned long flags; | |
188 | ||
189 | /* Fast path - period didn't change */ | |
190 | if (pl->period == period) | |
191 | return; | |
192 | raw_spin_lock_irqsave(&pl->lock, flags); | |
193 | /* Someone updated pl->period while we were spinning? */ | |
194 | if (pl->period >= period) { | |
195 | raw_spin_unlock_irqrestore(&pl->lock, flags); | |
196 | return; | |
197 | } | |
198 | /* Aging zeroed our fraction? */ | |
199 | if (period - pl->period < BITS_PER_LONG) { | |
200 | s64 val = percpu_counter_read(&pl->events); | |
201 | ||
202 | if (val < (nr_cpu_ids * PROP_BATCH)) | |
203 | val = percpu_counter_sum(&pl->events); | |
204 | ||
104b4e51 | 205 | percpu_counter_add_batch(&pl->events, |
f3109a51 JK |
206 | -val + (val >> (period-pl->period)), PROP_BATCH); |
207 | } else | |
208 | percpu_counter_set(&pl->events, 0); | |
209 | pl->period = period; | |
210 | raw_spin_unlock_irqrestore(&pl->lock, flags); | |
211 | } | |
212 | ||
213 | /* Event of type pl happened */ | |
be5f1797 MWO |
214 | void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl, |
215 | long nr) | |
f3109a51 JK |
216 | { |
217 | fprop_reflect_period_percpu(p, pl); | |
be5f1797 MWO |
218 | percpu_counter_add_batch(&pl->events, nr, PROP_BATCH); |
219 | percpu_counter_add(&p->events, nr); | |
f3109a51 JK |
220 | } |
221 | ||
222 | void fprop_fraction_percpu(struct fprop_global *p, | |
223 | struct fprop_local_percpu *pl, | |
224 | unsigned long *numerator, unsigned long *denominator) | |
225 | { | |
226 | unsigned int seq; | |
227 | s64 num, den; | |
228 | ||
229 | do { | |
230 | seq = read_seqcount_begin(&p->sequence); | |
231 | fprop_reflect_period_percpu(p, pl); | |
232 | num = percpu_counter_read_positive(&pl->events); | |
233 | den = percpu_counter_read_positive(&p->events); | |
234 | } while (read_seqcount_retry(&p->sequence, seq)); | |
235 | ||
236 | /* | |
237 | * Make fraction <= 1 and denominator > 0 even in presence of percpu | |
238 | * counter errors | |
239 | */ | |
240 | if (den <= num) { | |
241 | if (num) | |
242 | den = num; | |
243 | else | |
244 | den = 1; | |
245 | } | |
246 | *denominator = den; | |
247 | *numerator = num; | |
248 | } | |
249 | ||
250 | /* | |
be5f1797 | 251 | * Like __fprop_add_percpu() except that event is counted only if the given |
f3109a51 JK |
252 | * type has fraction smaller than @max_frac/FPROP_FRAC_BASE |
253 | */ | |
be5f1797 MWO |
254 | void __fprop_add_percpu_max(struct fprop_global *p, |
255 | struct fprop_local_percpu *pl, int max_frac, long nr) | |
f3109a51 JK |
256 | { |
257 | if (unlikely(max_frac < FPROP_FRAC_BASE)) { | |
258 | unsigned long numerator, denominator; | |
be5f1797 | 259 | s64 tmp; |
f3109a51 JK |
260 | |
261 | fprop_fraction_percpu(p, pl, &numerator, &denominator); | |
be5f1797 MWO |
262 | /* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */ |
263 | tmp = (u64)denominator * max_frac - | |
264 | ((u64)numerator << FPROP_FRAC_SHIFT); | |
265 | if (tmp < 0) { | |
266 | /* Maximum fraction already exceeded? */ | |
f3109a51 | 267 | return; |
be5f1797 MWO |
268 | } else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) { |
269 | /* Add just enough for the fraction to saturate */ | |
270 | nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1, | |
271 | FPROP_FRAC_BASE - max_frac); | |
272 | } | |
63d7f816 TH |
273 | } |
274 | ||
be5f1797 | 275 | __fprop_add_percpu(p, pl, nr); |
f3109a51 | 276 | } |