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-rw-r--r--lib/flex_proportions.c272
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1/*
2 * Floating proportions with flexible aging period
3 *
4 * Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
5 *
6 * The goal of this code is: Given different types of event, measure proportion
7 * of each type of event over time. The proportions are measured with
8 * exponentially decaying history to give smooth transitions. A formula
9 * expressing proportion of event of type 'j' is:
10 *
11 * p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
12 *
13 * Where x_{i,j} is j's number of events in i-th last time period and x_i is
14 * total number of events in i-th last time period.
15 *
16 * Note that p_{j}'s are normalised, i.e.
17 *
18 * \Sum_{j} p_{j} = 1,
19 *
20 * This formula can be straightforwardly computed by maintaing denominator
21 * (let's call it 'd') and for each event type its numerator (let's call it
22 * 'n_j'). When an event of type 'j' happens, we simply need to do:
23 * n_j++; d++;
24 *
25 * When a new period is declared, we could do:
26 * d /= 2
27 * for each j
28 * n_j /= 2
29 *
30 * To avoid iteration over all event types, we instead shift numerator of event
31 * j lazily when someone asks for a proportion of event j or when event j
32 * occurs. This can bit trivially implemented by remembering last period in
33 * which something happened with proportion of type j.
34 */
35#include <linux/flex_proportions.h>
36
37int fprop_global_init(struct fprop_global *p)
38{
39 int err;
40
41 p->period = 0;
42 /* Use 1 to avoid dealing with periods with 0 events... */
43 err = percpu_counter_init(&p->events, 1);
44 if (err)
45 return err;
46 seqcount_init(&p->sequence);
47 return 0;
48}
49
50void fprop_global_destroy(struct fprop_global *p)
51{
52 percpu_counter_destroy(&p->events);
53}
54
55/*
56 * Declare @periods new periods. It is upto the caller to make sure period
57 * transitions cannot happen in parallel.
58 *
59 * The function returns true if the proportions are still defined and false
60 * if aging zeroed out all events. This can be used to detect whether declaring
61 * further periods has any effect.
62 */
63bool fprop_new_period(struct fprop_global *p, int periods)
64{
65 u64 events;
66 unsigned long flags;
67
68 local_irq_save(flags);
69 events = percpu_counter_sum(&p->events);
70 /*
71 * Don't do anything if there are no events.
72 */
73 if (events <= 1) {
74 local_irq_restore(flags);
75 return false;
76 }
77 write_seqcount_begin(&p->sequence);
78 if (periods < 64)
79 events -= events >> periods;
80 /* Use addition to avoid losing events happening between sum and set */
81 percpu_counter_add(&p->events, -events);
82 p->period += periods;
83 write_seqcount_end(&p->sequence);
84 local_irq_restore(flags);
85
86 return true;
87}
88
89/*
90 * ---- SINGLE ----
91 */
92
93int fprop_local_init_single(struct fprop_local_single *pl)
94{
95 pl->events = 0;
96 pl->period = 0;
97 raw_spin_lock_init(&pl->lock);
98 return 0;
99}
100
101void fprop_local_destroy_single(struct fprop_local_single *pl)
102{
103}
104
105static void fprop_reflect_period_single(struct fprop_global *p,
106 struct fprop_local_single *pl)
107{
108 unsigned int period = p->period;
109 unsigned long flags;
110
111 /* Fast path - period didn't change */
112 if (pl->period == period)
113 return;
114 raw_spin_lock_irqsave(&pl->lock, flags);
115 /* Someone updated pl->period while we were spinning? */
116 if (pl->period >= period) {
117 raw_spin_unlock_irqrestore(&pl->lock, flags);
118 return;
119 }
120 /* Aging zeroed our fraction? */
121 if (period - pl->period < BITS_PER_LONG)
122 pl->events >>= period - pl->period;
123 else
124 pl->events = 0;
125 pl->period = period;
126 raw_spin_unlock_irqrestore(&pl->lock, flags);
127}
128
129/* Event of type pl happened */
130void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
131{
132 fprop_reflect_period_single(p, pl);
133 pl->events++;
134 percpu_counter_add(&p->events, 1);
135}
136
137/* Return fraction of events of type pl */
138void fprop_fraction_single(struct fprop_global *p,
139 struct fprop_local_single *pl,
140 unsigned long *numerator, unsigned long *denominator)
141{
142 unsigned int seq;
143 s64 num, den;
144
145 do {
146 seq = read_seqcount_begin(&p->sequence);
147 fprop_reflect_period_single(p, pl);
148 num = pl->events;
149 den = percpu_counter_read_positive(&p->events);
150 } while (read_seqcount_retry(&p->sequence, seq));
151
152 /*
153 * Make fraction <= 1 and denominator > 0 even in presence of percpu
154 * counter errors
155 */
156 if (den <= num) {
157 if (num)
158 den = num;
159 else
160 den = 1;
161 }
162 *denominator = den;
163 *numerator = num;
164}
165
166/*
167 * ---- PERCPU ----
168 */
169#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
170
171int fprop_local_init_percpu(struct fprop_local_percpu *pl)
172{
173 int err;
174
175 err = percpu_counter_init(&pl->events, 0);
176 if (err)
177 return err;
178 pl->period = 0;
179 raw_spin_lock_init(&pl->lock);
180 return 0;
181}
182
183void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
184{
185 percpu_counter_destroy(&pl->events);
186}
187
188static void fprop_reflect_period_percpu(struct fprop_global *p,
189 struct fprop_local_percpu *pl)
190{
191 unsigned int period = p->period;
192 unsigned long flags;
193
194 /* Fast path - period didn't change */
195 if (pl->period == period)
196 return;
197 raw_spin_lock_irqsave(&pl->lock, flags);
198 /* Someone updated pl->period while we were spinning? */
199 if (pl->period >= period) {
200 raw_spin_unlock_irqrestore(&pl->lock, flags);
201 return;
202 }
203 /* Aging zeroed our fraction? */
204 if (period - pl->period < BITS_PER_LONG) {
205 s64 val = percpu_counter_read(&pl->events);
206
207 if (val < (nr_cpu_ids * PROP_BATCH))
208 val = percpu_counter_sum(&pl->events);
209
210 __percpu_counter_add(&pl->events,
211 -val + (val >> (period-pl->period)), PROP_BATCH);
212 } else
213 percpu_counter_set(&pl->events, 0);
214 pl->period = period;
215 raw_spin_unlock_irqrestore(&pl->lock, flags);
216}
217
218/* Event of type pl happened */
219void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
220{
221 fprop_reflect_period_percpu(p, pl);
222 __percpu_counter_add(&pl->events, 1, PROP_BATCH);
223 percpu_counter_add(&p->events, 1);
224}
225
226void fprop_fraction_percpu(struct fprop_global *p,
227 struct fprop_local_percpu *pl,
228 unsigned long *numerator, unsigned long *denominator)
229{
230 unsigned int seq;
231 s64 num, den;
232
233 do {
234 seq = read_seqcount_begin(&p->sequence);
235 fprop_reflect_period_percpu(p, pl);
236 num = percpu_counter_read_positive(&pl->events);
237 den = percpu_counter_read_positive(&p->events);
238 } while (read_seqcount_retry(&p->sequence, seq));
239
240 /*
241 * Make fraction <= 1 and denominator > 0 even in presence of percpu
242 * counter errors
243 */
244 if (den <= num) {
245 if (num)
246 den = num;
247 else
248 den = 1;
249 }
250 *denominator = den;
251 *numerator = num;
252}
253
254/*
255 * Like __fprop_inc_percpu() except that event is counted only if the given
256 * type has fraction smaller than @max_frac/FPROP_FRAC_BASE
257 */
258void __fprop_inc_percpu_max(struct fprop_global *p,
259 struct fprop_local_percpu *pl, int max_frac)
260{
261 if (unlikely(max_frac < FPROP_FRAC_BASE)) {
262 unsigned long numerator, denominator;
263
264 fprop_fraction_percpu(p, pl, &numerator, &denominator);
265 if (numerator >
266 (((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
267 return;
268 } else
269 fprop_reflect_period_percpu(p, pl);
270 __percpu_counter_add(&pl->events, 1, PROP_BATCH);
271 percpu_counter_add(&p->events, 1);
272}
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