]>
git.proxmox.com Git - mirror_ubuntu-kernels.git/blob - lib/flex_proportions.c
1 // SPDX-License-Identifier: GPL-2.0
3 * Floating proportions with flexible aging period
5 * Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
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:
12 * p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
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.
17 * Note that p_{j}'s are normalised, i.e.
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:
26 * When a new period is declared, we could do:
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.
36 #include <linux/flex_proportions.h>
38 int fprop_global_init(struct fprop_global
*p
, gfp_t gfp
)
43 /* Use 1 to avoid dealing with periods with 0 events... */
44 err
= percpu_counter_init(&p
->events
, 1, gfp
);
47 seqcount_init(&p
->sequence
);
51 void fprop_global_destroy(struct fprop_global
*p
)
53 percpu_counter_destroy(&p
->events
);
57 * Declare @periods new periods. It is upto the caller to make sure period
58 * transitions cannot happen in parallel.
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.
64 bool fprop_new_period(struct fprop_global
*p
, int periods
)
66 s64 events
= percpu_counter_sum(&p
->events
);
69 * Don't do anything if there are no events.
73 preempt_disable_nested();
74 write_seqcount_begin(&p
->sequence
);
76 events
-= events
>> periods
;
77 /* Use addition to avoid losing events happening between sum and set */
78 percpu_counter_add(&p
->events
, -events
);
80 write_seqcount_end(&p
->sequence
);
81 preempt_enable_nested();
90 int fprop_local_init_single(struct fprop_local_single
*pl
)
94 raw_spin_lock_init(&pl
->lock
);
98 void fprop_local_destroy_single(struct fprop_local_single
*pl
)
102 static void fprop_reflect_period_single(struct fprop_global
*p
,
103 struct fprop_local_single
*pl
)
105 unsigned int period
= p
->period
;
108 /* Fast path - period didn't change */
109 if (pl
->period
== period
)
111 raw_spin_lock_irqsave(&pl
->lock
, flags
);
112 /* Someone updated pl->period while we were spinning? */
113 if (pl
->period
>= period
) {
114 raw_spin_unlock_irqrestore(&pl
->lock
, flags
);
117 /* Aging zeroed our fraction? */
118 if (period
- pl
->period
< BITS_PER_LONG
)
119 pl
->events
>>= period
- pl
->period
;
123 raw_spin_unlock_irqrestore(&pl
->lock
, flags
);
126 /* Event of type pl happened */
127 void __fprop_inc_single(struct fprop_global
*p
, struct fprop_local_single
*pl
)
129 fprop_reflect_period_single(p
, pl
);
131 percpu_counter_add(&p
->events
, 1);
134 /* Return fraction of events of type pl */
135 void fprop_fraction_single(struct fprop_global
*p
,
136 struct fprop_local_single
*pl
,
137 unsigned long *numerator
, unsigned long *denominator
)
143 seq
= read_seqcount_begin(&p
->sequence
);
144 fprop_reflect_period_single(p
, pl
);
146 den
= percpu_counter_read_positive(&p
->events
);
147 } while (read_seqcount_retry(&p
->sequence
, seq
));
150 * Make fraction <= 1 and denominator > 0 even in presence of percpu
166 #define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
168 int fprop_local_init_percpu(struct fprop_local_percpu
*pl
, gfp_t gfp
)
172 err
= percpu_counter_init(&pl
->events
, 0, gfp
);
176 raw_spin_lock_init(&pl
->lock
);
180 void fprop_local_destroy_percpu(struct fprop_local_percpu
*pl
)
182 percpu_counter_destroy(&pl
->events
);
185 static void fprop_reflect_period_percpu(struct fprop_global
*p
,
186 struct fprop_local_percpu
*pl
)
188 unsigned int period
= p
->period
;
191 /* Fast path - period didn't change */
192 if (pl
->period
== period
)
194 raw_spin_lock_irqsave(&pl
->lock
, flags
);
195 /* Someone updated pl->period while we were spinning? */
196 if (pl
->period
>= period
) {
197 raw_spin_unlock_irqrestore(&pl
->lock
, flags
);
200 /* Aging zeroed our fraction? */
201 if (period
- pl
->period
< BITS_PER_LONG
) {
202 s64 val
= percpu_counter_read(&pl
->events
);
204 if (val
< (nr_cpu_ids
* PROP_BATCH
))
205 val
= percpu_counter_sum(&pl
->events
);
207 percpu_counter_add_batch(&pl
->events
,
208 -val
+ (val
>> (period
-pl
->period
)), PROP_BATCH
);
210 percpu_counter_set(&pl
->events
, 0);
212 raw_spin_unlock_irqrestore(&pl
->lock
, flags
);
215 /* Event of type pl happened */
216 void __fprop_add_percpu(struct fprop_global
*p
, struct fprop_local_percpu
*pl
,
219 fprop_reflect_period_percpu(p
, pl
);
220 percpu_counter_add_batch(&pl
->events
, nr
, PROP_BATCH
);
221 percpu_counter_add(&p
->events
, nr
);
224 void fprop_fraction_percpu(struct fprop_global
*p
,
225 struct fprop_local_percpu
*pl
,
226 unsigned long *numerator
, unsigned long *denominator
)
232 seq
= read_seqcount_begin(&p
->sequence
);
233 fprop_reflect_period_percpu(p
, pl
);
234 num
= percpu_counter_read_positive(&pl
->events
);
235 den
= percpu_counter_read_positive(&p
->events
);
236 } while (read_seqcount_retry(&p
->sequence
, seq
));
239 * Make fraction <= 1 and denominator > 0 even in presence of percpu
253 * Like __fprop_add_percpu() except that event is counted only if the given
254 * type has fraction smaller than @max_frac/FPROP_FRAC_BASE
256 void __fprop_add_percpu_max(struct fprop_global
*p
,
257 struct fprop_local_percpu
*pl
, int max_frac
, long nr
)
259 if (unlikely(max_frac
< FPROP_FRAC_BASE
)) {
260 unsigned long numerator
, denominator
;
263 fprop_fraction_percpu(p
, pl
, &numerator
, &denominator
);
264 /* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */
265 tmp
= (u64
)denominator
* max_frac
-
266 ((u64
)numerator
<< FPROP_FRAC_SHIFT
);
268 /* Maximum fraction already exceeded? */
270 } else if (tmp
< nr
* (FPROP_FRAC_BASE
- max_frac
)) {
271 /* Add just enough for the fraction to saturate */
272 nr
= div_u64(tmp
+ FPROP_FRAC_BASE
- max_frac
- 1,
273 FPROP_FRAC_BASE
- max_frac
);
277 __fprop_add_percpu(p
, pl
, nr
);