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1// SPDX-License-Identifier: GPL-2.02/*3 * Floating proportions with flexible aging period4 *5 * Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>6 *7 * The goal of this code is: Given different types of event, measure proportion8 * of each type of event over time. The proportions are measured with9 * exponentially decaying history to give smooth transitions. A formula10 * 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 is15 * 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 denominator22 * (let's call it 'd') and for each event type its numerator (let's call it23 * '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 /= 228 * for each j29 * n_j /= 230 *31 * To avoid iteration over all event types, we instead shift numerator of event32 * j lazily when someone asks for a proportion of event j or when event j33 * occurs. This can bit trivially implemented by remembering last period in34 * which something happened with proportion of type j.35 */36#include <linux/flex_proportions.h>37 38int 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 51void 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 period58 * transitions cannot happen in parallel.59 *60 * The function returns true if the proportions are still defined and false61 * if aging zeroed out all events. This can be used to detect whether declaring62 * further periods has any effect.63 */64bool 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 91int 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 103void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)104{105 percpu_counter_destroy(&pl->events);106}107 108static 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 } else133 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 */139void __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 147void 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 percpu163 * counter errors164 */165 if (den <= num) {166 if (num)167 den = num;168 else169 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 given177 * type has fraction smaller than @max_frac/FPROP_FRAC_BASE178 */179void __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