Line data Source code
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 :
37 1 : int fprop_global_init(struct fprop_global *p, gfp_t gfp)
38 : {
39 : int err;
40 :
41 1 : p->period = 0;
42 : /* Use 1 to avoid dealing with periods with 0 events... */
43 : err = percpu_counter_init(&p->events, 1, gfp);
44 : if (err)
45 : return err;
46 : seqcount_init(&p->sequence);
47 : return 0;
48 : }
49 :
50 0 : void fprop_global_destroy(struct fprop_global *p)
51 : {
52 : percpu_counter_destroy(&p->events);
53 0 : }
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 : */
63 193 : bool fprop_new_period(struct fprop_global *p, int periods)
64 : {
65 : s64 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 : */
73 193 : if (events <= 1) {
74 44 : local_irq_restore(flags);
75 : return false;
76 : }
77 : write_seqcount_begin(&p->sequence);
78 149 : if (periods < 64)
79 149 : events -= events >> periods;
80 : /* Use addition to avoid losing events happening between sum and set */
81 : percpu_counter_add(&p->events, -events);
82 149 : p->period += periods;
83 : write_seqcount_end(&p->sequence);
84 149 : local_irq_restore(flags);
85 :
86 : return true;
87 : }
88 :
89 : /*
90 : * ---- SINGLE ----
91 : */
92 :
93 0 : int fprop_local_init_single(struct fprop_local_single *pl)
94 : {
95 0 : pl->events = 0;
96 0 : pl->period = 0;
97 : raw_spin_lock_init(&pl->lock);
98 0 : return 0;
99 : }
100 :
101 0 : void fprop_local_destroy_single(struct fprop_local_single *pl)
102 : {
103 0 : }
104 :
105 0 : static void fprop_reflect_period_single(struct fprop_global *p,
106 : struct fprop_local_single *pl)
107 : {
108 0 : unsigned int period = p->period;
109 : unsigned long flags;
110 :
111 : /* Fast path - period didn't change */
112 0 : if (pl->period == period)
113 : return;
114 0 : raw_spin_lock_irqsave(&pl->lock, flags);
115 : /* Someone updated pl->period while we were spinning? */
116 0 : if (pl->period >= period) {
117 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
118 : return;
119 : }
120 : /* Aging zeroed our fraction? */
121 0 : if (period - pl->period < BITS_PER_LONG)
122 0 : pl->events >>= period - pl->period;
123 : else
124 0 : pl->events = 0;
125 0 : pl->period = period;
126 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
127 : }
128 :
129 : /* Event of type pl happened */
130 0 : void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
131 : {
132 0 : fprop_reflect_period_single(p, pl);
133 0 : pl->events++;
134 : percpu_counter_add(&p->events, 1);
135 0 : }
136 :
137 : /* Return fraction of events of type pl */
138 0 : void 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 0 : fprop_reflect_period_single(p, pl);
148 0 : num = pl->events;
149 : den = percpu_counter_read_positive(&p->events);
150 0 : } 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 0 : if (den <= num) {
157 0 : if (num)
158 : den = num;
159 : else
160 : den = 1;
161 : }
162 0 : *denominator = den;
163 0 : *numerator = num;
164 0 : }
165 :
166 : /*
167 : * ---- PERCPU ----
168 : */
169 : #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
170 :
171 35 : int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
172 : {
173 : int err;
174 :
175 : err = percpu_counter_init(&pl->events, 0, gfp);
176 : if (err)
177 : return err;
178 35 : pl->period = 0;
179 : raw_spin_lock_init(&pl->lock);
180 : return 0;
181 : }
182 :
183 0 : void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
184 : {
185 : percpu_counter_destroy(&pl->events);
186 0 : }
187 :
188 5706 : static void fprop_reflect_period_percpu(struct fprop_global *p,
189 : struct fprop_local_percpu *pl)
190 : {
191 5706 : unsigned int period = p->period;
192 : unsigned long flags;
193 :
194 : /* Fast path - period didn't change */
195 5706 : if (pl->period == period)
196 : return;
197 95 : raw_spin_lock_irqsave(&pl->lock, flags);
198 : /* Someone updated pl->period while we were spinning? */
199 95 : if (pl->period >= period) {
200 0 : raw_spin_unlock_irqrestore(&pl->lock, flags);
201 : return;
202 : }
203 : /* Aging zeroed our fraction? */
204 95 : 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 95 : __percpu_counter_add(&pl->events,
211 95 : -val + (val >> (period-pl->period)), PROP_BATCH);
212 : } else
213 : percpu_counter_set(&pl->events, 0);
214 95 : pl->period = period;
215 285 : raw_spin_unlock_irqrestore(&pl->lock, flags);
216 : }
217 :
218 : /* Event of type pl happened */
219 0 : void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
220 : {
221 0 : fprop_reflect_period_percpu(p, pl);
222 : __percpu_counter_add(&pl->events, 1, PROP_BATCH);
223 : percpu_counter_add(&p->events, 1);
224 0 : }
225 :
226 482 : void 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);
235 241 : fprop_reflect_period_percpu(p, pl);
236 : num = percpu_counter_read_positive(&pl->events);
237 : den = percpu_counter_read_positive(&p->events);
238 241 : } 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 : */
244 241 : if (den <= num) {
245 241 : if (num)
246 : den = num;
247 : else
248 : den = 1;
249 : }
250 241 : *denominator = den;
251 241 : *numerator = num;
252 241 : }
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 : */
258 10930 : void __fprop_inc_percpu_max(struct fprop_global *p,
259 : struct fprop_local_percpu *pl, int max_frac)
260 : {
261 5465 : if (unlikely(max_frac < FPROP_FRAC_BASE)) {
262 : unsigned long numerator, denominator;
263 :
264 0 : fprop_fraction_percpu(p, pl, &numerator, &denominator);
265 0 : if (numerator >
266 0 : (((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
267 5465 : return;
268 : } else
269 5465 : 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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