Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/lib/flex_proportions.c

  1 /*
  2  *  Floating proportions with flexible aging period
  3  *
  4  *   Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
  5  *
  6  * The goal of this code is: Given different types of event, measure proportion
  7  * of each type of event over time. The proportions are measured with
  8  * exponentially decaying history to give smooth transitions. A formula
  9  * expressing proportion of event of type 'j' is:
 10  *
 11  *   p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
 12  *
 13  * Where x_{i,j} is j's number of events in i-th last time period and x_i is
 14  * total number of events in i-th last time period.
 15  *
 16  * Note that p_{j}'s are normalised, i.e.
 17  *
 18  *   \Sum_{j} p_{j} = 1,
 19  *
 20  * This formula can be straightforwardly computed by maintaining denominator
 21  * (let's call it 'd') and for each event type its numerator (let's call it
 22  * 'n_j'). When an event of type 'j' happens, we simply need to do:
 23  *   n_j++; d++;
 24  *
 25  * When a new period is declared, we could do:
 26  *   d /= 2
 27  *   for each j
 28  *     n_j /= 2
 29  *
 30  * To avoid iteration over all event types, we instead shift numerator of event
 31  * j lazily when someone asks for a proportion of event j or when event j
 32  * occurs. This can bit trivially implemented by remembering last period in
 33  * which something happened with proportion of type j.
 34  */
 35 #include <linux/flex_proportions.h>
 36 
 37 int fprop_global_init(struct fprop_global *p, gfp_t gfp)
 38 {
 39         int err;
 40 
 41         p->period = 0;
 42         /* Use 1 to avoid dealing with periods with 0 events... */
 43         err = percpu_counter_init(&p->events, 1, gfp);
 44         if (err)
 45                 return err;
 46         seqcount_init(&p->sequence);
 47         return 0;
 48 }
 49 
 50 void fprop_global_destroy(struct fprop_global *p)
 51 {
 52         percpu_counter_destroy(&p->events);
 53 }
 54 
 55 /*
 56  * Declare @periods new periods. It is upto the caller to make sure period
 57  * transitions cannot happen in parallel.
 58  *
 59  * The function returns true if the proportions are still defined and false
 60  * if aging zeroed out all events. This can be used to detect whether declaring
 61  * further periods has any effect.
 62  */
 63 bool fprop_new_period(struct fprop_global *p, int periods)
 64 {
 65         s64 events;
 66         unsigned long flags;
 67 
 68         local_irq_save(flags);
 69         events = percpu_counter_sum(&p->events);
 70         /*
 71          * Don't do anything if there are no events.
 72          */
 73         if (events <= 1) {
 74                 local_irq_restore(flags);
 75                 return false;
 76         }
 77         write_seqcount_begin(&p->sequence);
 78         if (periods < 64)
 79                 events -= events >> periods;
 80         /* Use addition to avoid losing events happening between sum and set */
 81         percpu_counter_add(&p->events, -events);
 82         p->period += periods;
 83         write_seqcount_end(&p->sequence);
 84         local_irq_restore(flags);
 85 
 86         return true;
 87 }
 88 
 89 /*
 90  * ---- SINGLE ----
 91  */
 92 
 93 int fprop_local_init_single(struct fprop_local_single *pl)
 94 {
 95         pl->events = 0;
 96         pl->period = 0;
 97         raw_spin_lock_init(&pl->lock);
 98         return 0;
 99 }
100 
101 void fprop_local_destroy_single(struct fprop_local_single *pl)
102 {
103 }
104 
105 static void fprop_reflect_period_single(struct fprop_global *p,
106                                         struct fprop_local_single *pl)
107 {
108         unsigned int period = p->period;
109         unsigned long flags;
110 
111         /* Fast path - period didn't change */
112         if (pl->period == period)
113                 return;
114         raw_spin_lock_irqsave(&pl->lock, flags);
115         /* Someone updated pl->period while we were spinning? */
116         if (pl->period >= period) {
117                 raw_spin_unlock_irqrestore(&pl->lock, flags);
118                 return;
119         }
120         /* Aging zeroed our fraction? */
121         if (period - pl->period < BITS_PER_LONG)
122                 pl->events >>= period - pl->period;
123         else
124                 pl->events = 0;
125         pl->period = period;
126         raw_spin_unlock_irqrestore(&pl->lock, flags);
127 }
128 
129 /* Event of type pl happened */
130 void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
131 {
132         fprop_reflect_period_single(p, pl);
133         pl->events++;
134         percpu_counter_add(&p->events, 1);
135 }
136 
137 /* Return fraction of events of type pl */
138 void fprop_fraction_single(struct fprop_global *p,
139                            struct fprop_local_single *pl,
140                            unsigned long *numerator, unsigned long *denominator)
141 {
142         unsigned int seq;
143         s64 num, den;
144 
145         do {
146                 seq = read_seqcount_begin(&p->sequence);
147                 fprop_reflect_period_single(p, pl);
148                 num = pl->events;
149                 den = percpu_counter_read_positive(&p->events);
150         } while (read_seqcount_retry(&p->sequence, seq));
151 
152         /*
153          * Make fraction <= 1 and denominator > 0 even in presence of percpu
154          * counter errors
155          */
156         if (den <= num) {
157                 if (num)
158                         den = num;
159                 else
160                         den = 1;
161         }
162         *denominator = den;
163         *numerator = num;
164 }
165 
166 /*
167  * ---- PERCPU ----
168  */
169 #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
170 
171 int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
172 {
173         int err;
174 
175         err = percpu_counter_init(&pl->events, 0, gfp);
176         if (err)
177                 return err;
178         pl->period = 0;
179         raw_spin_lock_init(&pl->lock);
180         return 0;
181 }
182 
183 void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
184 {
185         percpu_counter_destroy(&pl->events);
186 }
187 
188 static void fprop_reflect_period_percpu(struct fprop_global *p,
189                                         struct fprop_local_percpu *pl)
190 {
191         unsigned int period = p->period;
192         unsigned long flags;
193 
194         /* Fast path - period didn't change */
195         if (pl->period == period)
196                 return;
197         raw_spin_lock_irqsave(&pl->lock, flags);
198         /* Someone updated pl->period while we were spinning? */
199         if (pl->period >= period) {
200                 raw_spin_unlock_irqrestore(&pl->lock, flags);
201                 return;
202         }
203         /* Aging zeroed our fraction? */
204         if (period - pl->period < BITS_PER_LONG) {
205                 s64 val = percpu_counter_read(&pl->events);
206 
207                 if (val < (nr_cpu_ids * PROP_BATCH))
208                         val = percpu_counter_sum(&pl->events);
209 
210                 __percpu_counter_add(&pl->events,
211                         -val + (val >> (period-pl->period)), PROP_BATCH);
212         } else
213                 percpu_counter_set(&pl->events, 0);
214         pl->period = period;
215         raw_spin_unlock_irqrestore(&pl->lock, flags);
216 }
217 
218 /* Event of type pl happened */
219 void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
220 {
221         fprop_reflect_period_percpu(p, pl);
222         __percpu_counter_add(&pl->events, 1, PROP_BATCH);
223         percpu_counter_add(&p->events, 1);
224 }
225 
226 void fprop_fraction_percpu(struct fprop_global *p,
227                            struct fprop_local_percpu *pl,
228                            unsigned long *numerator, unsigned long *denominator)
229 {
230         unsigned int seq;
231         s64 num, den;
232 
233         do {
234                 seq = read_seqcount_begin(&p->sequence);
235                 fprop_reflect_period_percpu(p, pl);
236                 num = percpu_counter_read_positive(&pl->events);
237                 den = percpu_counter_read_positive(&p->events);
238         } while (read_seqcount_retry(&p->sequence, seq));
239 
240         /*
241          * Make fraction <= 1 and denominator > 0 even in presence of percpu
242          * counter errors
243          */
244         if (den <= num) {
245                 if (num)
246                         den = num;
247                 else
248                         den = 1;
249         }
250         *denominator = den;
251         *numerator = num;
252 }
253 
254 /*
255  * Like __fprop_inc_percpu() except that event is counted only if the given
256  * type has fraction smaller than @max_frac/FPROP_FRAC_BASE
257  */
258 void __fprop_inc_percpu_max(struct fprop_global *p,
259                             struct fprop_local_percpu *pl, int max_frac)
260 {
261         if (unlikely(max_frac < FPROP_FRAC_BASE)) {
262                 unsigned long numerator, denominator;
263 
264                 fprop_fraction_percpu(p, pl, &numerator, &denominator);
265                 if (numerator >
266                     (((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
267                         return;
268         } else
269                 fprop_reflect_period_percpu(p, pl);
270         __percpu_counter_add(&pl->events, 1, PROP_BATCH);
271         percpu_counter_add(&p->events, 1);
272 }
273 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us