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1 | /* | |
2 | * Fast batching percpu counters. | |
3 | */ | |
4 | ||
5 | #include <linux/percpu_counter.h> | |
6 | #include <linux/notifier.h> | |
7 | #include <linux/mutex.h> | |
8 | #include <linux/init.h> | |
9 | #include <linux/cpu.h> | |
10 | #include <linux/module.h> | |
11 | #include <linux/debugobjects.h> | |
12 | ||
13 | #ifdef CONFIG_HOTPLUG_CPU | |
14 | static LIST_HEAD(percpu_counters); | |
15 | static DEFINE_SPINLOCK(percpu_counters_lock); | |
16 | #endif | |
17 | ||
18 | #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER | |
19 | ||
20 | static struct debug_obj_descr percpu_counter_debug_descr; | |
21 | ||
22 | static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state) | |
23 | { | |
24 | struct percpu_counter *fbc = addr; | |
25 | ||
26 | switch (state) { | |
27 | case ODEBUG_STATE_ACTIVE: | |
28 | percpu_counter_destroy(fbc); | |
29 | debug_object_free(fbc, &percpu_counter_debug_descr); | |
30 | return true; | |
31 | default: | |
32 | return false; | |
33 | } | |
34 | } | |
35 | ||
36 | static struct debug_obj_descr percpu_counter_debug_descr = { | |
37 | .name = "percpu_counter", | |
38 | .fixup_free = percpu_counter_fixup_free, | |
39 | }; | |
40 | ||
41 | static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) | |
42 | { | |
43 | debug_object_init(fbc, &percpu_counter_debug_descr); | |
44 | debug_object_activate(fbc, &percpu_counter_debug_descr); | |
45 | } | |
46 | ||
47 | static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) | |
48 | { | |
49 | debug_object_deactivate(fbc, &percpu_counter_debug_descr); | |
50 | debug_object_free(fbc, &percpu_counter_debug_descr); | |
51 | } | |
52 | ||
53 | #else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ | |
54 | static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) | |
55 | { } | |
56 | static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) | |
57 | { } | |
58 | #endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ | |
59 | ||
60 | void percpu_counter_set(struct percpu_counter *fbc, s64 amount) | |
61 | { | |
62 | int cpu; | |
63 | unsigned long flags; | |
64 | ||
65 | raw_spin_lock_irqsave(&fbc->lock, flags); | |
66 | for_each_possible_cpu(cpu) { | |
67 | s32 *pcount = per_cpu_ptr(fbc->counters, cpu); | |
68 | *pcount = 0; | |
69 | } | |
70 | fbc->count = amount; | |
71 | raw_spin_unlock_irqrestore(&fbc->lock, flags); | |
72 | } | |
73 | EXPORT_SYMBOL(percpu_counter_set); | |
74 | ||
75 | /** | |
76 | * This function is both preempt and irq safe. The former is due to explicit | |
77 | * preemption disable. The latter is guaranteed by the fact that the slow path | |
78 | * is explicitly protected by an irq-safe spinlock whereas the fast patch uses | |
79 | * this_cpu_add which is irq-safe by definition. Hence there is no need muck | |
80 | * with irq state before calling this one | |
81 | */ | |
82 | void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) | |
83 | { | |
84 | s64 count; | |
85 | ||
86 | preempt_disable(); | |
87 | count = __this_cpu_read(*fbc->counters) + amount; | |
88 | if (count >= batch || count <= -batch) { | |
89 | unsigned long flags; | |
90 | raw_spin_lock_irqsave(&fbc->lock, flags); | |
91 | fbc->count += count; | |
92 | __this_cpu_sub(*fbc->counters, count - amount); | |
93 | raw_spin_unlock_irqrestore(&fbc->lock, flags); | |
94 | } else { | |
95 | this_cpu_add(*fbc->counters, amount); | |
96 | } | |
97 | preempt_enable(); | |
98 | } | |
99 | EXPORT_SYMBOL(percpu_counter_add_batch); | |
100 | ||
101 | /* | |
102 | * Add up all the per-cpu counts, return the result. This is a more accurate | |
103 | * but much slower version of percpu_counter_read_positive() | |
104 | */ | |
105 | s64 __percpu_counter_sum(struct percpu_counter *fbc) | |
106 | { | |
107 | s64 ret; | |
108 | int cpu; | |
109 | unsigned long flags; | |
110 | ||
111 | raw_spin_lock_irqsave(&fbc->lock, flags); | |
112 | ret = fbc->count; | |
113 | for_each_online_cpu(cpu) { | |
114 | s32 *pcount = per_cpu_ptr(fbc->counters, cpu); | |
115 | ret += *pcount; | |
116 | } | |
117 | raw_spin_unlock_irqrestore(&fbc->lock, flags); | |
118 | return ret; | |
119 | } | |
120 | EXPORT_SYMBOL(__percpu_counter_sum); | |
121 | ||
122 | int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, | |
123 | struct lock_class_key *key) | |
124 | { | |
125 | unsigned long flags __maybe_unused; | |
126 | ||
127 | raw_spin_lock_init(&fbc->lock); | |
128 | lockdep_set_class(&fbc->lock, key); | |
129 | fbc->count = amount; | |
130 | fbc->counters = alloc_percpu_gfp(s32, gfp); | |
131 | if (!fbc->counters) | |
132 | return -ENOMEM; | |
133 | ||
134 | debug_percpu_counter_activate(fbc); | |
135 | ||
136 | #ifdef CONFIG_HOTPLUG_CPU | |
137 | INIT_LIST_HEAD(&fbc->list); | |
138 | spin_lock_irqsave(&percpu_counters_lock, flags); | |
139 | list_add(&fbc->list, &percpu_counters); | |
140 | spin_unlock_irqrestore(&percpu_counters_lock, flags); | |
141 | #endif | |
142 | return 0; | |
143 | } | |
144 | EXPORT_SYMBOL(__percpu_counter_init); | |
145 | ||
146 | void percpu_counter_destroy(struct percpu_counter *fbc) | |
147 | { | |
148 | unsigned long flags __maybe_unused; | |
149 | ||
150 | if (!fbc->counters) | |
151 | return; | |
152 | ||
153 | debug_percpu_counter_deactivate(fbc); | |
154 | ||
155 | #ifdef CONFIG_HOTPLUG_CPU | |
156 | spin_lock_irqsave(&percpu_counters_lock, flags); | |
157 | list_del(&fbc->list); | |
158 | spin_unlock_irqrestore(&percpu_counters_lock, flags); | |
159 | #endif | |
160 | free_percpu(fbc->counters); | |
161 | fbc->counters = NULL; | |
162 | } | |
163 | EXPORT_SYMBOL(percpu_counter_destroy); | |
164 | ||
165 | int percpu_counter_batch __read_mostly = 32; | |
166 | EXPORT_SYMBOL(percpu_counter_batch); | |
167 | ||
168 | static int compute_batch_value(unsigned int cpu) | |
169 | { | |
170 | int nr = num_online_cpus(); | |
171 | ||
172 | percpu_counter_batch = max(32, nr*2); | |
173 | return 0; | |
174 | } | |
175 | ||
176 | static int percpu_counter_cpu_dead(unsigned int cpu) | |
177 | { | |
178 | #ifdef CONFIG_HOTPLUG_CPU | |
179 | struct percpu_counter *fbc; | |
180 | ||
181 | compute_batch_value(cpu); | |
182 | ||
183 | spin_lock_irq(&percpu_counters_lock); | |
184 | list_for_each_entry(fbc, &percpu_counters, list) { | |
185 | s32 *pcount; | |
186 | ||
187 | raw_spin_lock(&fbc->lock); | |
188 | pcount = per_cpu_ptr(fbc->counters, cpu); | |
189 | fbc->count += *pcount; | |
190 | *pcount = 0; | |
191 | raw_spin_unlock(&fbc->lock); | |
192 | } | |
193 | spin_unlock_irq(&percpu_counters_lock); | |
194 | #endif | |
195 | return 0; | |
196 | } | |
197 | ||
198 | /* | |
199 | * Compare counter against given value. | |
200 | * Return 1 if greater, 0 if equal and -1 if less | |
201 | */ | |
202 | int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) | |
203 | { | |
204 | s64 count; | |
205 | ||
206 | count = percpu_counter_read(fbc); | |
207 | /* Check to see if rough count will be sufficient for comparison */ | |
208 | if (abs(count - rhs) > (batch * num_online_cpus())) { | |
209 | if (count > rhs) | |
210 | return 1; | |
211 | else | |
212 | return -1; | |
213 | } | |
214 | /* Need to use precise count */ | |
215 | count = percpu_counter_sum(fbc); | |
216 | if (count > rhs) | |
217 | return 1; | |
218 | else if (count < rhs) | |
219 | return -1; | |
220 | else | |
221 | return 0; | |
222 | } | |
223 | EXPORT_SYMBOL(__percpu_counter_compare); | |
224 | ||
225 | static int __init percpu_counter_startup(void) | |
226 | { | |
227 | int ret; | |
228 | ||
229 | ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", | |
230 | compute_batch_value, NULL); | |
231 | WARN_ON(ret < 0); | |
232 | ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, | |
233 | "lib/percpu_cnt:dead", NULL, | |
234 | percpu_counter_cpu_dead); | |
235 | WARN_ON(ret < 0); | |
236 | return 0; | |
237 | } | |
238 | module_init(percpu_counter_startup); |