1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Fast batching percpu counters.
4  */
5 
6 #include <linux/percpu_counter.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 const struct debug_obj_descr percpu_counter_debug_descr;
21 
percpu_counter_fixup_free(void * addr,enum debug_obj_state state)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 const struct debug_obj_descr percpu_counter_debug_descr = {
37 	.name		= "percpu_counter",
38 	.fixup_free	= percpu_counter_fixup_free,
39 };
40 
debug_percpu_counter_activate(struct percpu_counter * fbc)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 
debug_percpu_counter_deactivate(struct percpu_counter * fbc)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 */
debug_percpu_counter_activate(struct percpu_counter * fbc)54 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
55 { }
debug_percpu_counter_deactivate(struct percpu_counter * fbc)56 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
57 { }
58 #endif	/* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
59 
percpu_counter_set(struct percpu_counter * fbc,s64 amount)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  */
percpu_counter_add_batch(struct percpu_counter * fbc,s64 amount,s32 batch)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 (abs(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  * For percpu_counter with a big batch, the devication of its count could
103  * be big, and there is requirement to reduce the deviation, like when the
104  * counter's batch could be runtime decreased to get a better accuracy,
105  * which can be achieved by running this sync function on each CPU.
106  */
percpu_counter_sync(struct percpu_counter * fbc)107 void percpu_counter_sync(struct percpu_counter *fbc)
108 {
109 	unsigned long flags;
110 	s64 count;
111 
112 	raw_spin_lock_irqsave(&fbc->lock, flags);
113 	count = __this_cpu_read(*fbc->counters);
114 	fbc->count += count;
115 	__this_cpu_sub(*fbc->counters, count);
116 	raw_spin_unlock_irqrestore(&fbc->lock, flags);
117 }
118 EXPORT_SYMBOL(percpu_counter_sync);
119 
120 /*
121  * Add up all the per-cpu counts, return the result.  This is a more accurate
122  * but much slower version of percpu_counter_read_positive()
123  */
__percpu_counter_sum(struct percpu_counter * fbc)124 s64 __percpu_counter_sum(struct percpu_counter *fbc)
125 {
126 	s64 ret;
127 	int cpu;
128 	unsigned long flags;
129 
130 	raw_spin_lock_irqsave(&fbc->lock, flags);
131 	ret = fbc->count;
132 	for_each_online_cpu(cpu) {
133 		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
134 		ret += *pcount;
135 	}
136 	raw_spin_unlock_irqrestore(&fbc->lock, flags);
137 	return ret;
138 }
139 EXPORT_SYMBOL(__percpu_counter_sum);
140 
__percpu_counter_init(struct percpu_counter * fbc,s64 amount,gfp_t gfp,struct lock_class_key * key)141 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
142 			  struct lock_class_key *key)
143 {
144 	unsigned long flags __maybe_unused;
145 
146 	raw_spin_lock_init(&fbc->lock);
147 	lockdep_set_class(&fbc->lock, key);
148 	fbc->count = amount;
149 	fbc->counters = alloc_percpu_gfp(s32, gfp);
150 	if (!fbc->counters)
151 		return -ENOMEM;
152 
153 	debug_percpu_counter_activate(fbc);
154 
155 #ifdef CONFIG_HOTPLUG_CPU
156 	INIT_LIST_HEAD(&fbc->list);
157 	spin_lock_irqsave(&percpu_counters_lock, flags);
158 	list_add(&fbc->list, &percpu_counters);
159 	spin_unlock_irqrestore(&percpu_counters_lock, flags);
160 #endif
161 	return 0;
162 }
163 EXPORT_SYMBOL(__percpu_counter_init);
164 
percpu_counter_destroy(struct percpu_counter * fbc)165 void percpu_counter_destroy(struct percpu_counter *fbc)
166 {
167 	unsigned long flags __maybe_unused;
168 
169 	if (!fbc->counters)
170 		return;
171 
172 	debug_percpu_counter_deactivate(fbc);
173 
174 #ifdef CONFIG_HOTPLUG_CPU
175 	spin_lock_irqsave(&percpu_counters_lock, flags);
176 	list_del(&fbc->list);
177 	spin_unlock_irqrestore(&percpu_counters_lock, flags);
178 #endif
179 	free_percpu(fbc->counters);
180 	fbc->counters = NULL;
181 }
182 EXPORT_SYMBOL(percpu_counter_destroy);
183 
184 int percpu_counter_batch __read_mostly = 32;
185 EXPORT_SYMBOL(percpu_counter_batch);
186 
compute_batch_value(unsigned int cpu)187 static int compute_batch_value(unsigned int cpu)
188 {
189 	int nr = num_online_cpus();
190 
191 	percpu_counter_batch = max(32, nr*2);
192 	return 0;
193 }
194 
percpu_counter_cpu_dead(unsigned int cpu)195 static int percpu_counter_cpu_dead(unsigned int cpu)
196 {
197 #ifdef CONFIG_HOTPLUG_CPU
198 	struct percpu_counter *fbc;
199 
200 	compute_batch_value(cpu);
201 
202 	spin_lock_irq(&percpu_counters_lock);
203 	list_for_each_entry(fbc, &percpu_counters, list) {
204 		s32 *pcount;
205 
206 		raw_spin_lock(&fbc->lock);
207 		pcount = per_cpu_ptr(fbc->counters, cpu);
208 		fbc->count += *pcount;
209 		*pcount = 0;
210 		raw_spin_unlock(&fbc->lock);
211 	}
212 	spin_unlock_irq(&percpu_counters_lock);
213 #endif
214 	return 0;
215 }
216 
217 /*
218  * Compare counter against given value.
219  * Return 1 if greater, 0 if equal and -1 if less
220  */
__percpu_counter_compare(struct percpu_counter * fbc,s64 rhs,s32 batch)221 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
222 {
223 	s64	count;
224 
225 	count = percpu_counter_read(fbc);
226 	/* Check to see if rough count will be sufficient for comparison */
227 	if (abs(count - rhs) > (batch * num_online_cpus())) {
228 		if (count > rhs)
229 			return 1;
230 		else
231 			return -1;
232 	}
233 	/* Need to use precise count */
234 	count = percpu_counter_sum(fbc);
235 	if (count > rhs)
236 		return 1;
237 	else if (count < rhs)
238 		return -1;
239 	else
240 		return 0;
241 }
242 EXPORT_SYMBOL(__percpu_counter_compare);
243 
percpu_counter_startup(void)244 static int __init percpu_counter_startup(void)
245 {
246 	int ret;
247 
248 	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
249 				compute_batch_value, NULL);
250 	WARN_ON(ret < 0);
251 	ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
252 					"lib/percpu_cnt:dead", NULL,
253 					percpu_counter_cpu_dead);
254 	WARN_ON(ret < 0);
255 	return 0;
256 }
257 module_init(percpu_counter_startup);
258