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1 | /* |
2 | * Atomic operations on 64-bit quantities. | |
3 | * | |
4 | * Copyright (C) 2017 Red Hat, Inc. | |
5 | * | |
6 | * Author: Paolo Bonzini <pbonzini@redhat.com> | |
7 | * | |
8 | * This work is licensed under the terms of the GNU GPL, version 2 or later. | |
9 | * See the COPYING file in the top-level directory. | |
10 | */ | |
11 | ||
12 | #ifndef QEMU_STATS64_H | |
177d9e0d | 13 | #define QEMU_STATS64_H |
ae2d489c PB |
14 | |
15 | #include "qemu/atomic.h" | |
16 | ||
17 | /* This provides atomic operations on 64-bit type, using a reader-writer | |
18 | * spinlock on architectures that do not have 64-bit accesses. Even on | |
19 | * those architectures, it tries hard not to take the lock. | |
20 | */ | |
21 | ||
22 | typedef struct Stat64 { | |
23 | #ifdef CONFIG_ATOMIC64 | |
9ef0c6d6 | 24 | aligned_uint64_t value; |
ae2d489c PB |
25 | #else |
26 | uint32_t low, high; | |
27 | uint32_t lock; | |
28 | #endif | |
29 | } Stat64; | |
30 | ||
31 | #ifdef CONFIG_ATOMIC64 | |
32 | static inline void stat64_init(Stat64 *s, uint64_t value) | |
33 | { | |
34 | /* This is not guaranteed to be atomic! */ | |
35 | *s = (Stat64) { value }; | |
36 | } | |
37 | ||
38 | static inline uint64_t stat64_get(const Stat64 *s) | |
39 | { | |
d73415a3 | 40 | return qatomic_read__nocheck(&s->value); |
ae2d489c PB |
41 | } |
42 | ||
7757b55e PB |
43 | static inline void stat64_set(Stat64 *s, uint64_t value) |
44 | { | |
45 | qatomic_set__nocheck(&s->value, value); | |
46 | } | |
47 | ||
ae2d489c PB |
48 | static inline void stat64_add(Stat64 *s, uint64_t value) |
49 | { | |
d73415a3 | 50 | qatomic_add(&s->value, value); |
ae2d489c PB |
51 | } |
52 | ||
53 | static inline void stat64_min(Stat64 *s, uint64_t value) | |
54 | { | |
d73415a3 | 55 | uint64_t orig = qatomic_read__nocheck(&s->value); |
ae2d489c | 56 | while (orig > value) { |
d73415a3 | 57 | orig = qatomic_cmpxchg__nocheck(&s->value, orig, value); |
ae2d489c PB |
58 | } |
59 | } | |
60 | ||
61 | static inline void stat64_max(Stat64 *s, uint64_t value) | |
62 | { | |
d73415a3 | 63 | uint64_t orig = qatomic_read__nocheck(&s->value); |
ae2d489c | 64 | while (orig < value) { |
d73415a3 | 65 | orig = qatomic_cmpxchg__nocheck(&s->value, orig, value); |
ae2d489c PB |
66 | } |
67 | } | |
68 | #else | |
69 | uint64_t stat64_get(const Stat64 *s); | |
7757b55e | 70 | void stat64_set(Stat64 *s, uint64_t value); |
ae2d489c PB |
71 | bool stat64_min_slow(Stat64 *s, uint64_t value); |
72 | bool stat64_max_slow(Stat64 *s, uint64_t value); | |
73 | bool stat64_add32_carry(Stat64 *s, uint32_t low, uint32_t high); | |
74 | ||
75 | static inline void stat64_init(Stat64 *s, uint64_t value) | |
76 | { | |
77 | /* This is not guaranteed to be atomic! */ | |
78 | *s = (Stat64) { .low = value, .high = value >> 32, .lock = 0 }; | |
79 | } | |
80 | ||
81 | static inline void stat64_add(Stat64 *s, uint64_t value) | |
82 | { | |
83 | uint32_t low, high; | |
84 | high = value >> 32; | |
85 | low = (uint32_t) value; | |
86 | if (!low) { | |
87 | if (high) { | |
d73415a3 | 88 | qatomic_add(&s->high, high); |
ae2d489c PB |
89 | } |
90 | return; | |
91 | } | |
92 | ||
93 | for (;;) { | |
94 | uint32_t orig = s->low; | |
95 | uint32_t result = orig + low; | |
96 | uint32_t old; | |
97 | ||
98 | if (result < low || high) { | |
99 | /* If the high part is affected, take the lock. */ | |
100 | if (stat64_add32_carry(s, low, high)) { | |
101 | return; | |
102 | } | |
103 | continue; | |
104 | } | |
105 | ||
106 | /* No carry, try with a 32-bit cmpxchg. The result is independent of | |
107 | * the high 32 bits, so it can race just fine with stat64_add32_carry | |
108 | * and even stat64_get! | |
109 | */ | |
d73415a3 | 110 | old = qatomic_cmpxchg(&s->low, orig, result); |
ae2d489c PB |
111 | if (orig == old) { |
112 | return; | |
113 | } | |
114 | } | |
115 | } | |
116 | ||
117 | static inline void stat64_min(Stat64 *s, uint64_t value) | |
118 | { | |
119 | uint32_t low, high; | |
120 | uint32_t orig_low, orig_high; | |
121 | ||
122 | high = value >> 32; | |
123 | low = (uint32_t) value; | |
124 | do { | |
d73415a3 | 125 | orig_high = qatomic_read(&s->high); |
ae2d489c PB |
126 | if (orig_high < high) { |
127 | return; | |
128 | } | |
129 | ||
130 | if (orig_high == high) { | |
131 | /* High 32 bits are equal. Read low after high, otherwise we | |
132 | * can get a false positive (e.g. 0x1235,0x0000 changes to | |
133 | * 0x1234,0x8000 and we read it as 0x1234,0x0000). Pairs with | |
134 | * the write barrier in stat64_min_slow. | |
135 | */ | |
136 | smp_rmb(); | |
d73415a3 | 137 | orig_low = qatomic_read(&s->low); |
ae2d489c PB |
138 | if (orig_low <= low) { |
139 | return; | |
140 | } | |
141 | ||
142 | /* See if we were lucky and a writer raced against us. The | |
143 | * barrier is theoretically unnecessary, but if we remove it | |
144 | * we may miss being lucky. | |
145 | */ | |
146 | smp_rmb(); | |
d73415a3 | 147 | orig_high = qatomic_read(&s->high); |
ae2d489c PB |
148 | if (orig_high < high) { |
149 | return; | |
150 | } | |
151 | } | |
152 | ||
153 | /* If the value changes in any way, we have to take the lock. */ | |
154 | } while (!stat64_min_slow(s, value)); | |
155 | } | |
156 | ||
157 | static inline void stat64_max(Stat64 *s, uint64_t value) | |
158 | { | |
159 | uint32_t low, high; | |
160 | uint32_t orig_low, orig_high; | |
161 | ||
162 | high = value >> 32; | |
163 | low = (uint32_t) value; | |
164 | do { | |
d73415a3 | 165 | orig_high = qatomic_read(&s->high); |
ae2d489c PB |
166 | if (orig_high > high) { |
167 | return; | |
168 | } | |
169 | ||
170 | if (orig_high == high) { | |
171 | /* High 32 bits are equal. Read low after high, otherwise we | |
172 | * can get a false positive (e.g. 0x1234,0x8000 changes to | |
173 | * 0x1235,0x0000 and we read it as 0x1235,0x8000). Pairs with | |
174 | * the write barrier in stat64_max_slow. | |
175 | */ | |
176 | smp_rmb(); | |
d73415a3 | 177 | orig_low = qatomic_read(&s->low); |
ae2d489c PB |
178 | if (orig_low >= low) { |
179 | return; | |
180 | } | |
181 | ||
182 | /* See if we were lucky and a writer raced against us. The | |
183 | * barrier is theoretically unnecessary, but if we remove it | |
184 | * we may miss being lucky. | |
185 | */ | |
186 | smp_rmb(); | |
d73415a3 | 187 | orig_high = qatomic_read(&s->high); |
ae2d489c PB |
188 | if (orig_high > high) { |
189 | return; | |
190 | } | |
191 | } | |
192 | ||
193 | /* If the value changes in any way, we have to take the lock. */ | |
194 | } while (!stat64_max_slow(s, value)); | |
195 | } | |
196 | ||
197 | #endif | |
198 | ||
199 | #endif |