diff options
Diffstat (limited to 'lib/flex_proportions.c')
| -rw-r--r-- | lib/flex_proportions.c | 266 |
1 files changed, 266 insertions, 0 deletions
diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c new file mode 100644 index 0000000..e02a388 --- /dev/null +++ b/lib/flex_proportions.c @@ -0,0 +1,266 @@ +/* + * Floating proportions with flexible aging period + * + * Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz> + * + * 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 <linux/flex_proportions.h> + +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) +{ + u64 events = percpu_counter_sum(&p->events); + + /* + * Don't do anything if there are no events. + */ + if (events <= 1) + 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); + + 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); +} |
