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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 | static LIST_HEAD(percpu_counters); |
14 | static DEFINE_MUTEX(percpu_counters_lock); |
15 | |
16 | #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER |
17 | |
18 | static struct debug_obj_descr percpu_counter_debug_descr; |
19 | |
20 | static int percpu_counter_fixup_free(void *addr, enum debug_obj_state state) |
21 | { |
22 | struct percpu_counter *fbc = addr; |
23 | |
24 | switch (state) { |
25 | case ODEBUG_STATE_ACTIVE: |
26 | percpu_counter_destroy(fbc); |
27 | debug_object_free(fbc, &percpu_counter_debug_descr); |
28 | return 1; |
29 | default: |
30 | return 0; |
31 | } |
32 | } |
33 | |
34 | static struct debug_obj_descr percpu_counter_debug_descr = { |
35 | .name = "percpu_counter", |
36 | .fixup_free = percpu_counter_fixup_free, |
37 | }; |
38 | |
39 | static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) |
40 | { |
41 | debug_object_init(fbc, &percpu_counter_debug_descr); |
42 | debug_object_activate(fbc, &percpu_counter_debug_descr); |
43 | } |
44 | |
45 | static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) |
46 | { |
47 | debug_object_deactivate(fbc, &percpu_counter_debug_descr); |
48 | debug_object_free(fbc, &percpu_counter_debug_descr); |
49 | } |
50 | |
51 | #else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ |
52 | static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) |
53 | { } |
54 | static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) |
55 | { } |
56 | #endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ |
57 | |
58 | void percpu_counter_set(struct percpu_counter *fbc, s64 amount) |
59 | { |
60 | int cpu; |
61 | |
62 | spin_lock(&fbc->lock); |
63 | for_each_possible_cpu(cpu) { |
64 | s32 *pcount = per_cpu_ptr(fbc->counters, cpu); |
65 | *pcount = 0; |
66 | } |
67 | fbc->count = amount; |
68 | spin_unlock(&fbc->lock); |
69 | } |
70 | EXPORT_SYMBOL(percpu_counter_set); |
71 | |
72 | void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch) |
73 | { |
74 | s64 count; |
75 | |
76 | preempt_disable(); |
77 | count = __this_cpu_read(*fbc->counters) + amount; |
78 | if (count >= batch || count <= -batch) { |
79 | spin_lock(&fbc->lock); |
80 | fbc->count += count; |
81 | __this_cpu_write(*fbc->counters, 0); |
82 | spin_unlock(&fbc->lock); |
83 | } else { |
84 | __this_cpu_write(*fbc->counters, count); |
85 | } |
86 | preempt_enable(); |
87 | } |
88 | EXPORT_SYMBOL(__percpu_counter_add); |
89 | |
90 | /* |
91 | * Add up all the per-cpu counts, return the result. This is a more accurate |
92 | * but much slower version of percpu_counter_read_positive() |
93 | */ |
94 | s64 __percpu_counter_sum(struct percpu_counter *fbc) |
95 | { |
96 | s64 ret; |
97 | int cpu; |
98 | |
99 | spin_lock(&fbc->lock); |
100 | ret = fbc->count; |
101 | for_each_online_cpu(cpu) { |
102 | s32 *pcount = per_cpu_ptr(fbc->counters, cpu); |
103 | ret += *pcount; |
104 | } |
105 | spin_unlock(&fbc->lock); |
106 | return ret; |
107 | } |
108 | EXPORT_SYMBOL(__percpu_counter_sum); |
109 | |
110 | int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, |
111 | struct lock_class_key *key) |
112 | { |
113 | spin_lock_init(&fbc->lock); |
114 | lockdep_set_class(&fbc->lock, key); |
115 | fbc->count = amount; |
116 | fbc->counters = alloc_percpu(s32); |
117 | if (!fbc->counters) |
118 | return -ENOMEM; |
119 | |
120 | debug_percpu_counter_activate(fbc); |
121 | |
122 | #ifdef CONFIG_HOTPLUG_CPU |
123 | INIT_LIST_HEAD(&fbc->list); |
124 | mutex_lock(&percpu_counters_lock); |
125 | list_add(&fbc->list, &percpu_counters); |
126 | mutex_unlock(&percpu_counters_lock); |
127 | #endif |
128 | return 0; |
129 | } |
130 | EXPORT_SYMBOL(__percpu_counter_init); |
131 | |
132 | void percpu_counter_destroy(struct percpu_counter *fbc) |
133 | { |
134 | if (!fbc->counters) |
135 | return; |
136 | |
137 | debug_percpu_counter_deactivate(fbc); |
138 | |
139 | #ifdef CONFIG_HOTPLUG_CPU |
140 | mutex_lock(&percpu_counters_lock); |
141 | list_del(&fbc->list); |
142 | mutex_unlock(&percpu_counters_lock); |
143 | #endif |
144 | free_percpu(fbc->counters); |
145 | fbc->counters = NULL; |
146 | } |
147 | EXPORT_SYMBOL(percpu_counter_destroy); |
148 | |
149 | int percpu_counter_batch __read_mostly = 32; |
150 | EXPORT_SYMBOL(percpu_counter_batch); |
151 | |
152 | static void compute_batch_value(void) |
153 | { |
154 | int nr = num_online_cpus(); |
155 | |
156 | percpu_counter_batch = max(32, nr*2); |
157 | } |
158 | |
159 | static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb, |
160 | unsigned long action, void *hcpu) |
161 | { |
162 | #ifdef CONFIG_HOTPLUG_CPU |
163 | unsigned int cpu; |
164 | struct percpu_counter *fbc; |
165 | |
166 | compute_batch_value(); |
167 | if (action != CPU_DEAD) |
168 | return NOTIFY_OK; |
169 | |
170 | cpu = (unsigned long)hcpu; |
171 | mutex_lock(&percpu_counters_lock); |
172 | list_for_each_entry(fbc, &percpu_counters, list) { |
173 | s32 *pcount; |
174 | unsigned long flags; |
175 | |
176 | spin_lock_irqsave(&fbc->lock, flags); |
177 | pcount = per_cpu_ptr(fbc->counters, cpu); |
178 | fbc->count += *pcount; |
179 | *pcount = 0; |
180 | spin_unlock_irqrestore(&fbc->lock, flags); |
181 | } |
182 | mutex_unlock(&percpu_counters_lock); |
183 | #endif |
184 | return NOTIFY_OK; |
185 | } |
186 | |
187 | /* |
188 | * Compare counter against given value. |
189 | * Return 1 if greater, 0 if equal and -1 if less |
190 | */ |
191 | int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) |
192 | { |
193 | s64 count; |
194 | |
195 | count = percpu_counter_read(fbc); |
196 | /* Check to see if rough count will be sufficient for comparison */ |
197 | if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) { |
198 | if (count > rhs) |
199 | return 1; |
200 | else |
201 | return -1; |
202 | } |
203 | /* Need to use precise count */ |
204 | count = percpu_counter_sum(fbc); |
205 | if (count > rhs) |
206 | return 1; |
207 | else if (count < rhs) |
208 | return -1; |
209 | else |
210 | return 0; |
211 | } |
212 | EXPORT_SYMBOL(percpu_counter_compare); |
213 | |
214 | static int __init percpu_counter_startup(void) |
215 | { |
216 | compute_batch_value(); |
217 | hotcpu_notifier(percpu_counter_hotcpu_callback, 0); |
218 | return 0; |
219 | } |
220 | module_init(percpu_counter_startup); |
221 |
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