Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0
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 : *
21 : * This formula can be straightforwardly computed by maintaining denominator
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 :
38 1 : int fprop_global_init(struct fprop_global *p, gfp_t gfp)
39 : {
40 : int err;
41 :
42 1 : p->period = 0;
43 : /* Use 1 to avoid dealing with periods with 0 events... */
44 2 : err = percpu_counter_init(&p->events, 1, gfp);
45 : if (err)
46 : return err;
47 2 : seqcount_init(&p->sequence);
48 : return 0;
49 : }
50 :
51 0 : void fprop_global_destroy(struct fprop_global *p)
52 : {
53 0 : percpu_counter_destroy(&p->events);
54 0 : }
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 0 : bool fprop_new_period(struct fprop_global *p, int periods)
65 : {
66 0 : s64 events = percpu_counter_sum(&p->events);
67 :
68 : /*
69 : * Don't do anything if there are no events.
70 : */
71 0 : if (events <= 1)
72 : return false;
73 : preempt_disable_nested();
74 0 : write_seqcount_begin(&p->sequence);
75 0 : if (periods < 64)
76 0 : events -= events >> periods;
77 : /* Use addition to avoid losing events happening between sum and set */
78 0 : percpu_counter_add(&p->events, -events);
79 0 : p->period += periods;
80 0 : write_seqcount_end(&p->sequence);
81 : preempt_enable_nested();
82 :
83 0 : return true;
84 : }
85 :
86 : /*
87 : * ---- SINGLE ----
88 : */
89 :
90 0 : int fprop_local_init_single(struct fprop_local_single *pl)
91 : {
92 0 : pl->events = 0;
93 0 : pl->period = 0;
94 : raw_spin_lock_init(&pl->lock);
95 0 : return 0;
96 : }
97 :
98 0 : void fprop_local_destroy_single(struct fprop_local_single *pl)
99 : {
100 0 : }
101 :
102 0 : static void fprop_reflect_period_single(struct fprop_global *p,
103 : struct fprop_local_single *pl)
104 : {
105 0 : unsigned int period = p->period;
106 : unsigned long flags;
107 :
108 : /* Fast path - period didn't change */
109 0 : if (pl->period == period)
110 : return;
111 0 : raw_spin_lock_irqsave(&pl->lock, flags);
112 : /* Someone updated pl->period while we were spinning? */
113 0 : if (pl->period >= period) {
114 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
115 : return;
116 : }
117 : /* Aging zeroed our fraction? */
118 0 : if (period - pl->period < BITS_PER_LONG)
119 0 : pl->events >>= period - pl->period;
120 : else
121 0 : pl->events = 0;
122 0 : pl->period = period;
123 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
124 : }
125 :
126 : /* Event of type pl happened */
127 0 : void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
128 : {
129 0 : fprop_reflect_period_single(p, pl);
130 0 : pl->events++;
131 0 : percpu_counter_add(&p->events, 1);
132 0 : }
133 :
134 : /* Return fraction of events of type pl */
135 0 : void fprop_fraction_single(struct fprop_global *p,
136 : struct fprop_local_single *pl,
137 : unsigned long *numerator, unsigned long *denominator)
138 : {
139 : unsigned int seq;
140 : s64 num, den;
141 :
142 : do {
143 0 : seq = read_seqcount_begin(&p->sequence);
144 0 : fprop_reflect_period_single(p, pl);
145 0 : num = pl->events;
146 0 : den = percpu_counter_read_positive(&p->events);
147 0 : } while (read_seqcount_retry(&p->sequence, seq));
148 :
149 : /*
150 : * Make fraction <= 1 and denominator > 0 even in presence of percpu
151 : * counter errors
152 : */
153 0 : if (den <= num) {
154 0 : if (num)
155 : den = num;
156 : else
157 0 : den = 1;
158 : }
159 0 : *denominator = den;
160 0 : *numerator = num;
161 0 : }
162 :
163 : /*
164 : * ---- PERCPU ----
165 : */
166 : #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
167 :
168 1 : int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
169 : {
170 : int err;
171 :
172 2 : err = percpu_counter_init(&pl->events, 0, gfp);
173 : if (err)
174 : return err;
175 1 : pl->period = 0;
176 : raw_spin_lock_init(&pl->lock);
177 : return 0;
178 : }
179 :
180 0 : void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
181 : {
182 0 : percpu_counter_destroy(&pl->events);
183 0 : }
184 :
185 0 : static void fprop_reflect_period_percpu(struct fprop_global *p,
186 : struct fprop_local_percpu *pl)
187 : {
188 0 : unsigned int period = p->period;
189 : unsigned long flags;
190 :
191 : /* Fast path - period didn't change */
192 0 : if (pl->period == period)
193 : return;
194 0 : raw_spin_lock_irqsave(&pl->lock, flags);
195 : /* Someone updated pl->period while we were spinning? */
196 0 : if (pl->period >= period) {
197 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
198 : return;
199 : }
200 : /* Aging zeroed our fraction? */
201 0 : if (period - pl->period < BITS_PER_LONG) {
202 0 : s64 val = percpu_counter_read(&pl->events);
203 :
204 : if (val < (nr_cpu_ids * PROP_BATCH))
205 : val = percpu_counter_sum(&pl->events);
206 :
207 0 : percpu_counter_add_batch(&pl->events,
208 0 : -val + (val >> (period-pl->period)), PROP_BATCH);
209 : } else
210 0 : percpu_counter_set(&pl->events, 0);
211 0 : pl->period = period;
212 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
213 : }
214 :
215 : /* Event of type pl happened */
216 0 : void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl,
217 : long nr)
218 : {
219 0 : fprop_reflect_period_percpu(p, pl);
220 0 : percpu_counter_add_batch(&pl->events, nr, PROP_BATCH);
221 0 : percpu_counter_add(&p->events, nr);
222 0 : }
223 :
224 0 : void fprop_fraction_percpu(struct fprop_global *p,
225 : struct fprop_local_percpu *pl,
226 : unsigned long *numerator, unsigned long *denominator)
227 : {
228 : unsigned int seq;
229 : s64 num, den;
230 :
231 : do {
232 0 : seq = read_seqcount_begin(&p->sequence);
233 0 : fprop_reflect_period_percpu(p, pl);
234 0 : num = percpu_counter_read_positive(&pl->events);
235 0 : den = percpu_counter_read_positive(&p->events);
236 0 : } while (read_seqcount_retry(&p->sequence, seq));
237 :
238 : /*
239 : * Make fraction <= 1 and denominator > 0 even in presence of percpu
240 : * counter errors
241 : */
242 0 : if (den <= num) {
243 0 : if (num)
244 : den = num;
245 : else
246 0 : den = 1;
247 : }
248 0 : *denominator = den;
249 0 : *numerator = num;
250 0 : }
251 :
252 : /*
253 : * Like __fprop_add_percpu() except that event is counted only if the given
254 : * type has fraction smaller than @max_frac/FPROP_FRAC_BASE
255 : */
256 0 : void __fprop_add_percpu_max(struct fprop_global *p,
257 : struct fprop_local_percpu *pl, int max_frac, long nr)
258 : {
259 0 : if (unlikely(max_frac < FPROP_FRAC_BASE)) {
260 : unsigned long numerator, denominator;
261 : s64 tmp;
262 :
263 0 : fprop_fraction_percpu(p, pl, &numerator, &denominator);
264 : /* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */
265 0 : tmp = (u64)denominator * max_frac -
266 0 : ((u64)numerator << FPROP_FRAC_SHIFT);
267 0 : if (tmp < 0) {
268 : /* Maximum fraction already exceeded? */
269 0 : return;
270 0 : } else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) {
271 : /* Add just enough for the fraction to saturate */
272 0 : nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1,
273 : FPROP_FRAC_BASE - max_frac);
274 : }
275 : }
276 :
277 0 : __fprop_add_percpu(p, pl, nr);
278 : }
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