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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 | |
37 | int 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 | |
50 | void 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 | */ |
63 | 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 | 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 | |
93 | int 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 | |
101 | void fprop_local_destroy_single(struct fprop_local_single *pl) |
102 | { |
103 | } |
104 | |
105 | static 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 */ |
130 | void __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 */ |
138 | 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 | 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 | |
171 | int 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 | |
183 | void fprop_local_destroy_percpu(struct fprop_local_percpu *pl) |
184 | { |
185 | percpu_counter_destroy(&pl->events); |
186 | } |
187 | |
188 | static 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 */ |
219 | void __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 | |
226 | 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 | 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 | */ |
258 | void __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 | } |
273 |
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