Staging: comedi: fix mmap_count
[linux-2.6.git] / lib / percpu_counter.c
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);