/* * Floating proportions with flexible aging period * * Copyright (C) 2011, SUSE, Jan Kara * * The goal of this code is: Given different types of event, measure proportion * of each type of event over time. The proportions are measured with * exponentially decaying history to give smooth transitions. A formula * expressing proportion of event of type 'j' is: * * p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1}) * * Where x_{i,j} is j's number of events in i-th last time period and x_i is * total number of events in i-th last time period. * * Note that p_{j}'s are normalised, i.e. * * \Sum_{j} p_{j} = 1, * * This formula can be straightforwardly computed by maintaing denominator * (let's call it 'd') and for each event type its numerator (let's call it * 'n_j'). When an event of type 'j' happens, we simply need to do: * n_j++; d++; * * When a new period is declared, we could do: * d /= 2 * for each j * n_j /= 2 * * To avoid iteration over all event types, we instead shift numerator of event * j lazily when someone asks for a proportion of event j or when event j * occurs. This can bit trivially implemented by remembering last period in * which something happened with proportion of type j. */ #include int fprop_global_init(struct fprop_global *p) { int err; p->period = 0; /* Use 1 to avoid dealing with periods with 0 events... */ err = percpu_counter_init(&p->events, 1); if (err) return err; seqcount_init(&p->sequence); return 0; } void fprop_global_destroy(struct fprop_global *p) { percpu_counter_destroy(&p->events); } /* * Declare @periods new periods. It is upto the caller to make sure period * transitions cannot happen in parallel. * * The function returns true if the proportions are still defined and false * if aging zeroed out all events. This can be used to detect whether declaring * further periods has any effect. */ bool fprop_new_period(struct fprop_global *p, int periods) { s64 events; unsigned long flags; local_irq_save(flags); events = percpu_counter_sum(&p->events); /* * Don't do anything if there are no events. */ if (events <= 1) { local_irq_restore(flags); return false; } write_seqcount_begin(&p->sequence); if (periods < 64) events -= events >> periods; /* Use addition to avoid losing events happening between sum and set */ percpu_counter_add(&p->events, -events); p->period += periods; write_seqcount_end(&p->sequence); local_irq_restore(flags); return true; } /* * ---- SINGLE ---- */ int fprop_local_init_single(struct fprop_local_single *pl) { pl->events = 0; pl->period = 0; raw_spin_lock_init(&pl->lock); return 0; } void fprop_local_destroy_single(struct fprop_local_single *pl) { } static void fprop_reflect_period_single(struct fprop_global *p, struct fprop_local_single *pl) { unsigned int period = p->period; unsigned long flags; /* Fast path - period didn't change */ if (pl->period == period) return; raw_spin_lock_irqsave(&pl->lock, flags); /* Someone updated pl->period while we were spinning? */ if (pl->period >= period) { raw_spin_unlock_irqrestore(&pl->lock, flags); return; } /* Aging zeroed our fraction? */ if (period - pl->period < BITS_PER_LONG) pl->events >>= period - pl->period; else pl->events = 0; pl->period = period; raw_spin_unlock_irqrestore(&pl->lock, flags); } /* Event of type pl happened */ void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl) { fprop_reflect_period_single(p, pl); pl->events++; percpu_counter_add(&p->events, 1); } /* Return fraction of events of type pl */ void fprop_fraction_single(struct fprop_global *p, struct fprop_local_single *pl, unsigned long *numerator, unsigned long *denominator) { unsigned int seq; s64 num, den; do { seq = read_seqcount_begin(&p->sequence); fprop_reflect_period_single(p, pl); num = pl->events; den = percpu_counter_read_positive(&p->events); } while (read_seqcount_retry(&p->sequence, seq)); /* * Make fraction <= 1 and denominator > 0 even in presence of percpu * counter errors */ if (den <= num) { if (num) den = num; else den = 1; } *denominator = den; *numerator = num; } /* * ---- PERCPU ---- */ #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids))) int fprop_local_init_percpu(struct fprop_local_percpu *pl) { int err; err = percpu_counter_init(&pl->events, 0); if (err) return err; pl->period = 0; raw_spin_lock_init(&pl->lock); return 0; } void fprop_local_destroy_percpu(struct fprop_local_percpu *pl) { percpu_counter_destroy(&pl->events); } static void fprop_reflect_period_percpu(struct fprop_global *p, struct fprop_local_percpu *pl) { unsigned int period = p->period; unsigned long flags; /* Fast path - period didn't change */ if (pl->period == period) return; raw_spin_lock_irqsave(&pl->lock, flags); /* Someone updated pl->period while we were spinning? */ if (pl->period >= period) { raw_spin_unlock_irqrestore(&pl->lock, flags); return; } /* Aging zeroed our fraction? */ if (period - pl->period < BITS_PER_LONG) { s64 val = percpu_counter_read(&pl->events); if (val < (nr_cpu_ids * PROP_BATCH)) val = percpu_counter_sum(&pl->events); __percpu_counter_add(&pl->events, -val + (val >> (period-pl->period)), PROP_BATCH); } else percpu_counter_set(&pl->events, 0); pl->period = period; raw_spin_unlock_irqrestore(&pl->lock, flags); } /* Event of type pl happened */ void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl) { fprop_reflect_period_percpu(p, pl); __percpu_counter_add(&pl->events, 1, PROP_BATCH); percpu_counter_add(&p->events, 1); } void fprop_fraction_percpu(struct fprop_global *p, struct fprop_local_percpu *pl, unsigned long *numerator, unsigned long *denominator) { unsigned int seq; s64 num, den; do { seq = read_seqcount_begin(&p->sequence); fprop_reflect_period_percpu(p, pl); num = percpu_counter_read_positive(&pl->events); den = percpu_counter_read_positive(&p->events); } while (read_seqcount_retry(&p->sequence, seq)); /* * Make fraction <= 1 and denominator > 0 even in presence of percpu * counter errors */ if (den <= num) { if (num) den = num; else den = 1; } *denominator = den; *numerator = num; } /* * Like __fprop_inc_percpu() except that event is counted only if the given * type has fraction smaller than @max_frac/FPROP_FRAC_BASE */ void __fprop_inc_percpu_max(struct fprop_global *p, struct fprop_local_percpu *pl, int max_frac) { if (unlikely(max_frac < FPROP_FRAC_BASE)) { unsigned long numerator, denominator; fprop_fraction_percpu(p, pl, &numerator, &denominator); if (numerator > (((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT) return; } else fprop_reflect_period_percpu(p, pl); __percpu_counter_add(&pl->events, 1, PROP_BATCH); percpu_counter_add(&p->events, 1); }