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 int fprop_global_init(struct fprop_global *p, gfp_t gfp) 39 { 40 int err; 41 42 p->period = 0; 43 /* Use 1 to avoid dealing with periods with 0 events... */ 44 err = percpu_counter_init(&p->events, 1, gfp); 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 { 66 s64 events = percpu_counter_sum(&p->events); 67 68 /* 69 * Don't do anything if there are no events. 70 */ 71 if (events <= 1) 72 return false; 73 preempt_disable_nested(); 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); 81 preempt_enable_nested(); 82 83 return true; 84 } 85 86 /* 87 * ---- PERCPU ---- 88 */ 89 #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids))) 90 91 int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp) 92 { 93 int err; 94 95 err = percpu_counter_init(&pl->events, 0, gfp); 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); 129 130 percpu_counter_add_batch(&pl->events, 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 */ 139 void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl, 140 long nr) 141 { 142 fprop_reflect_period_percpu(p, pl); 143 percpu_counter_add_batch(&pl->events, nr, PROP_BATCH); 144 percpu_counter_add(&p->events, nr); 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 /* 176 * Like __fprop_add_percpu() except that event is counted only if the given 177 * type has fraction smaller than @max_frac/FPROP_FRAC_BASE 178 */ 179 void __fprop_add_percpu_max(struct fprop_global *p, 180 struct fprop_local_percpu *pl, int max_frac, long nr) 181 { 182 if (unlikely(max_frac < FPROP_FRAC_BASE)) { 183 unsigned long numerator, denominator; 184 s64 tmp; 185 186 fprop_fraction_percpu(p, pl, &numerator, &denominator); 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? */ 192 return; 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 } 198 } 199 200 __fprop_add_percpu(p, pl, nr); 201 } 202