138 lines
3.3 KiB
C
138 lines
3.3 KiB
C
/*
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* Atomic operations on 64-bit quantities.
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*
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* Copyright (C) 2017 Red Hat, Inc.
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "qemu/atomic.h"
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#include "qemu/stats64.h"
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#include "qemu/processor.h"
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#ifndef CONFIG_ATOMIC64
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static inline void stat64_rdlock(Stat64 *s)
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{
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/* Keep out incoming writers to avoid them starving us. */
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atomic_add(&s->lock, 2);
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/* If there is a concurrent writer, wait for it. */
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while (atomic_read(&s->lock) & 1) {
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cpu_relax();
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}
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}
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static inline void stat64_rdunlock(Stat64 *s)
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{
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atomic_sub(&s->lock, 2);
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}
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static inline bool stat64_wrtrylock(Stat64 *s)
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{
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return atomic_cmpxchg(&s->lock, 0, 1) == 0;
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}
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static inline void stat64_wrunlock(Stat64 *s)
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{
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atomic_dec(&s->lock);
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}
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uint64_t stat64_get(const Stat64 *s)
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{
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uint32_t high, low;
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stat64_rdlock((Stat64 *)s);
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/* 64-bit writes always take the lock, so we can read in
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* any order.
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*/
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high = atomic_read(&s->high);
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low = atomic_read(&s->low);
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stat64_rdunlock((Stat64 *)s);
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return ((uint64_t)high << 32) | low;
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}
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bool stat64_add32_carry(Stat64 *s, uint32_t low, uint32_t high)
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{
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uint32_t old;
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if (!stat64_wrtrylock(s)) {
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cpu_relax();
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return false;
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}
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/* 64-bit reads always take the lock, so they don't care about the
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* order of our update. By updating s->low first, we can check
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* whether we have to carry into s->high.
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*/
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old = atomic_fetch_add(&s->low, low);
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high += (old + low) < old;
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atomic_add(&s->high, high);
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stat64_wrunlock(s);
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return true;
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}
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bool stat64_min_slow(Stat64 *s, uint64_t value)
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{
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uint32_t high, low;
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uint64_t orig;
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if (!stat64_wrtrylock(s)) {
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cpu_relax();
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return false;
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}
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high = atomic_read(&s->high);
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low = atomic_read(&s->low);
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orig = ((uint64_t)high << 32) | low;
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if (value < orig) {
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/* We have to set low before high, just like stat64_min reads
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* high before low. The value may become higher temporarily, but
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* stat64_get does not notice (it takes the lock) and the only ill
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* effect on stat64_min is that the slow path may be triggered
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* unnecessarily.
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*/
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atomic_set(&s->low, (uint32_t)value);
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smp_wmb();
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atomic_set(&s->high, value >> 32);
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}
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stat64_wrunlock(s);
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return true;
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}
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bool stat64_max_slow(Stat64 *s, uint64_t value)
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{
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uint32_t high, low;
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uint64_t orig;
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if (!stat64_wrtrylock(s)) {
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cpu_relax();
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return false;
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}
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high = atomic_read(&s->high);
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low = atomic_read(&s->low);
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orig = ((uint64_t)high << 32) | low;
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if (value > orig) {
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/* We have to set low before high, just like stat64_max reads
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* high before low. The value may become lower temporarily, but
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* stat64_get does not notice (it takes the lock) and the only ill
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* effect on stat64_max is that the slow path may be triggered
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* unnecessarily.
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*/
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atomic_set(&s->low, (uint32_t)value);
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smp_wmb();
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atomic_set(&s->high, value >> 32);
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}
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stat64_wrunlock(s);
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return true;
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}
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#endif
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