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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);
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