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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 | 72 | return false; |
9458e0a7 | 73 | preempt_disable_nested(); |
f3109a51 JK |
74 | write_seqcount_begin(&p->sequence); |
75 | if (periods < 64) | |
76 | events -= events >> periods; | |
77 | /* Use addition to avoid losing events happening between sum and set */ | |
78 | percpu_counter_add(&p->events, -events); | |
79 | p->period += periods; | |
80 | write_seqcount_end(&p->sequence); | |
9458e0a7 | 81 | preempt_enable_nested(); |
f3109a51 JK |
82 | |
83 | return true; | |
84 | } | |
85 | ||
f3109a51 JK |
86 | /* |
87 | * ---- PERCPU ---- | |
88 | */ | |
89 | #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids))) | |
90 | ||
20ae0079 | 91 | int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp) |
f3109a51 JK |
92 | { |
93 | int err; | |
94 | ||
20ae0079 | 95 | err = percpu_counter_init(&pl->events, 0, gfp); |
f3109a51 JK |
96 | if (err) |
97 | return err; | |
98 | pl->period = 0; | |
99 | raw_spin_lock_init(&pl->lock); | |
100 | return 0; | |
101 | } | |
102 | ||
103 | void fprop_local_destroy_percpu(struct fprop_local_percpu *pl) | |
104 | { | |
105 | percpu_counter_destroy(&pl->events); | |
106 | } | |
107 | ||
108 | static void fprop_reflect_period_percpu(struct fprop_global *p, | |
109 | struct fprop_local_percpu *pl) | |
110 | { | |
111 | unsigned int period = p->period; | |
112 | unsigned long flags; | |
113 | ||
114 | /* Fast path - period didn't change */ | |
115 | if (pl->period == period) | |
116 | return; | |
117 | raw_spin_lock_irqsave(&pl->lock, flags); | |
118 | /* Someone updated pl->period while we were spinning? */ | |
119 | if (pl->period >= period) { | |
120 | raw_spin_unlock_irqrestore(&pl->lock, flags); | |
121 | return; | |
122 | } | |
123 | /* Aging zeroed our fraction? */ | |
124 | if (period - pl->period < BITS_PER_LONG) { | |
125 | s64 val = percpu_counter_read(&pl->events); | |
126 | ||
127 | if (val < (nr_cpu_ids * PROP_BATCH)) | |
128 | val = percpu_counter_sum(&pl->events); | |
129 | ||
104b4e51 | 130 | percpu_counter_add_batch(&pl->events, |
f3109a51 JK |
131 | -val + (val >> (period-pl->period)), PROP_BATCH); |
132 | } else | |
133 | percpu_counter_set(&pl->events, 0); | |
134 | pl->period = period; | |
135 | raw_spin_unlock_irqrestore(&pl->lock, flags); | |
136 | } | |
137 | ||
138 | /* Event of type pl happened */ | |
be5f1797 MWO |
139 | void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl, |
140 | long nr) | |
f3109a51 JK |
141 | { |
142 | fprop_reflect_period_percpu(p, pl); | |
be5f1797 MWO |
143 | percpu_counter_add_batch(&pl->events, nr, PROP_BATCH); |
144 | percpu_counter_add(&p->events, nr); | |
f3109a51 JK |
145 | } |
146 | ||
147 | void fprop_fraction_percpu(struct fprop_global *p, | |
148 | struct fprop_local_percpu *pl, | |
149 | unsigned long *numerator, unsigned long *denominator) | |
150 | { | |
151 | unsigned int seq; | |
152 | s64 num, den; | |
153 | ||
154 | do { | |
155 | seq = read_seqcount_begin(&p->sequence); | |
156 | fprop_reflect_period_percpu(p, pl); | |
157 | num = percpu_counter_read_positive(&pl->events); | |
158 | den = percpu_counter_read_positive(&p->events); | |
159 | } while (read_seqcount_retry(&p->sequence, seq)); | |
160 | ||
161 | /* | |
162 | * Make fraction <= 1 and denominator > 0 even in presence of percpu | |
163 | * counter errors | |
164 | */ | |
165 | if (den <= num) { | |
166 | if (num) | |
167 | den = num; | |
168 | else | |
169 | den = 1; | |
170 | } | |
171 | *denominator = den; | |
172 | *numerator = num; | |
173 | } | |
174 | ||
175 | /* | |
be5f1797 | 176 | * Like __fprop_add_percpu() except that event is counted only if the given |
f3109a51 JK |
177 | * type has fraction smaller than @max_frac/FPROP_FRAC_BASE |
178 | */ | |
be5f1797 MWO |
179 | void __fprop_add_percpu_max(struct fprop_global *p, |
180 | struct fprop_local_percpu *pl, int max_frac, long nr) | |
f3109a51 JK |
181 | { |
182 | if (unlikely(max_frac < FPROP_FRAC_BASE)) { | |
183 | unsigned long numerator, denominator; | |
be5f1797 | 184 | s64 tmp; |
f3109a51 JK |
185 | |
186 | fprop_fraction_percpu(p, pl, &numerator, &denominator); | |
be5f1797 MWO |
187 | /* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */ |
188 | tmp = (u64)denominator * max_frac - | |
189 | ((u64)numerator << FPROP_FRAC_SHIFT); | |
190 | if (tmp < 0) { | |
191 | /* Maximum fraction already exceeded? */ | |
f3109a51 | 192 | return; |
be5f1797 MWO |
193 | } else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) { |
194 | /* Add just enough for the fraction to saturate */ | |
195 | nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1, | |
196 | FPROP_FRAC_BASE - max_frac); | |
197 | } | |
63d7f816 TH |
198 | } |
199 | ||
be5f1797 | 200 | __fprop_add_percpu(p, pl, nr); |
f3109a51 | 201 | } |