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 #include "qemu/osdep.h" 13 #include "qemu/atomic.h" 14 #include "qemu/stats64.h" 15 #include "qemu/processor.h" 16 17 #ifndef CONFIG_ATOMIC64 18 static inline void stat64_rdlock(Stat64 *s) 19 { 20 /* Keep out incoming writers to avoid them starving us. */ 21 qatomic_add(&s->lock, 2); 22 23 /* If there is a concurrent writer, wait for it. */ 24 while (qatomic_read(&s->lock) & 1) { 25 cpu_relax(); 26 } 27 } 28 29 static inline void stat64_rdunlock(Stat64 *s) 30 { 31 qatomic_sub(&s->lock, 2); 32 } 33 34 static inline bool stat64_wrtrylock(Stat64 *s) 35 { 36 return qatomic_cmpxchg(&s->lock, 0, 1) == 0; 37 } 38 39 static inline void stat64_wrunlock(Stat64 *s) 40 { 41 qatomic_dec(&s->lock); 42 } 43 44 uint64_t stat64_get(const Stat64 *s) 45 { 46 uint32_t high, low; 47 48 stat64_rdlock((Stat64 *)s); 49 50 /* 64-bit writes always take the lock, so we can read in 51 * any order. 52 */ 53 high = qatomic_read(&s->high); 54 low = qatomic_read(&s->low); 55 stat64_rdunlock((Stat64 *)s); 56 57 return ((uint64_t)high << 32) | low; 58 } 59 60 bool stat64_add32_carry(Stat64 *s, uint32_t low, uint32_t high) 61 { 62 uint32_t old; 63 64 if (!stat64_wrtrylock(s)) { 65 cpu_relax(); 66 return false; 67 } 68 69 /* 64-bit reads always take the lock, so they don't care about the 70 * order of our update. By updating s->low first, we can check 71 * whether we have to carry into s->high. 72 */ 73 old = qatomic_fetch_add(&s->low, low); 74 high += (old + low) < old; 75 qatomic_add(&s->high, high); 76 stat64_wrunlock(s); 77 return true; 78 } 79 80 bool stat64_min_slow(Stat64 *s, uint64_t value) 81 { 82 uint32_t high, low; 83 uint64_t orig; 84 85 if (!stat64_wrtrylock(s)) { 86 cpu_relax(); 87 return false; 88 } 89 90 high = qatomic_read(&s->high); 91 low = qatomic_read(&s->low); 92 93 orig = ((uint64_t)high << 32) | low; 94 if (value < orig) { 95 /* We have to set low before high, just like stat64_min reads 96 * high before low. The value may become higher temporarily, but 97 * stat64_get does not notice (it takes the lock) and the only ill 98 * effect on stat64_min is that the slow path may be triggered 99 * unnecessarily. 100 */ 101 qatomic_set(&s->low, (uint32_t)value); 102 smp_wmb(); 103 qatomic_set(&s->high, value >> 32); 104 } 105 stat64_wrunlock(s); 106 return true; 107 } 108 109 bool stat64_max_slow(Stat64 *s, uint64_t value) 110 { 111 uint32_t high, low; 112 uint64_t orig; 113 114 if (!stat64_wrtrylock(s)) { 115 cpu_relax(); 116 return false; 117 } 118 119 high = qatomic_read(&s->high); 120 low = qatomic_read(&s->low); 121 122 orig = ((uint64_t)high << 32) | low; 123 if (value > orig) { 124 /* We have to set low before high, just like stat64_max reads 125 * high before low. The value may become lower temporarily, but 126 * stat64_get does not notice (it takes the lock) and the only ill 127 * effect on stat64_max is that the slow path may be triggered 128 * unnecessarily. 129 */ 130 qatomic_set(&s->low, (uint32_t)value); 131 smp_wmb(); 132 qatomic_set(&s->high, value >> 32); 133 } 134 stat64_wrunlock(s); 135 return true; 136 } 137 #endif 138