From e44e3482bdb4d0ebde2d8b41830ac2cdb07948fb Mon Sep 17 00:00:00 2001 From: Yang Zhang Date: Fri, 28 Aug 2015 09:58:54 +0800 Subject: Add qemu 2.4.0 Change-Id: Ic99cbad4b61f8b127b7dc74d04576c0bcbaaf4f5 Signed-off-by: Yang Zhang --- qemu/util/rcu.c | 330 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 330 insertions(+) create mode 100644 qemu/util/rcu.c (limited to 'qemu/util/rcu.c') diff --git a/qemu/util/rcu.c b/qemu/util/rcu.c new file mode 100644 index 000000000..cdcad678b --- /dev/null +++ b/qemu/util/rcu.c @@ -0,0 +1,330 @@ +/* + * urcu-mb.c + * + * Userspace RCU library with explicit memory barriers + * + * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. + * Copyright 2015 Red Hat, Inc. + * + * Ported to QEMU by Paolo Bonzini + * + * This library is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with this library; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + * + * IBM's contributions to this file may be relicensed under LGPLv2 or later. + */ + +#include "qemu-common.h" +#include +#include +#include +#include +#include +#include "qemu/rcu.h" +#include "qemu/atomic.h" +#include "qemu/thread.h" +#include "qemu/main-loop.h" + +/* + * Global grace period counter. Bit 0 is always one in rcu_gp_ctr. + * Bits 1 and above are defined in synchronize_rcu. + */ +#define RCU_GP_LOCKED (1UL << 0) +#define RCU_GP_CTR (1UL << 1) + +unsigned long rcu_gp_ctr = RCU_GP_LOCKED; + +QemuEvent rcu_gp_event; +static QemuMutex rcu_gp_lock; + +/* + * Check whether a quiescent state was crossed between the beginning of + * update_counter_and_wait and now. + */ +static inline int rcu_gp_ongoing(unsigned long *ctr) +{ + unsigned long v; + + v = atomic_read(ctr); + return v && (v != rcu_gp_ctr); +} + +/* Written to only by each individual reader. Read by both the reader and the + * writers. + */ +__thread struct rcu_reader_data rcu_reader; + +/* Protected by rcu_gp_lock. */ +typedef QLIST_HEAD(, rcu_reader_data) ThreadList; +static ThreadList registry = QLIST_HEAD_INITIALIZER(registry); + +/* Wait for previous parity/grace period to be empty of readers. */ +static void wait_for_readers(void) +{ + ThreadList qsreaders = QLIST_HEAD_INITIALIZER(qsreaders); + struct rcu_reader_data *index, *tmp; + + for (;;) { + /* We want to be notified of changes made to rcu_gp_ongoing + * while we walk the list. + */ + qemu_event_reset(&rcu_gp_event); + + /* Instead of using atomic_mb_set for index->waiting, and + * atomic_mb_read for index->ctr, memory barriers are placed + * manually since writes to different threads are independent. + * atomic_mb_set has a smp_wmb before... + */ + smp_wmb(); + QLIST_FOREACH(index, ®istry, node) { + atomic_set(&index->waiting, true); + } + + /* ... and a smp_mb after. */ + smp_mb(); + + QLIST_FOREACH_SAFE(index, ®istry, node, tmp) { + if (!rcu_gp_ongoing(&index->ctr)) { + QLIST_REMOVE(index, node); + QLIST_INSERT_HEAD(&qsreaders, index, node); + + /* No need for mb_set here, worst of all we + * get some extra futex wakeups. + */ + atomic_set(&index->waiting, false); + } + } + + /* atomic_mb_read has smp_rmb after. */ + smp_rmb(); + + if (QLIST_EMPTY(®istry)) { + break; + } + + /* Wait for one thread to report a quiescent state and + * try again. + */ + qemu_event_wait(&rcu_gp_event); + } + + /* put back the reader list in the registry */ + QLIST_SWAP(®istry, &qsreaders, node); +} + +void synchronize_rcu(void) +{ + qemu_mutex_lock(&rcu_gp_lock); + + if (!QLIST_EMPTY(®istry)) { + /* In either case, the atomic_mb_set below blocks stores that free + * old RCU-protected pointers. + */ + if (sizeof(rcu_gp_ctr) < 8) { + /* For architectures with 32-bit longs, a two-subphases algorithm + * ensures we do not encounter overflow bugs. + * + * Switch parity: 0 -> 1, 1 -> 0. + */ + atomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); + wait_for_readers(); + atomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); + } else { + /* Increment current grace period. */ + atomic_mb_set(&rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); + } + + wait_for_readers(); + } + + qemu_mutex_unlock(&rcu_gp_lock); +} + + +#define RCU_CALL_MIN_SIZE 30 + +/* Multi-producer, single-consumer queue based on urcu/static/wfqueue.h + * from liburcu. Note that head is only used by the consumer. + */ +static struct rcu_head dummy; +static struct rcu_head *head = &dummy, **tail = &dummy.next; +static int rcu_call_count; +static QemuEvent rcu_call_ready_event; + +static void enqueue(struct rcu_head *node) +{ + struct rcu_head **old_tail; + + node->next = NULL; + old_tail = atomic_xchg(&tail, &node->next); + atomic_mb_set(old_tail, node); +} + +static struct rcu_head *try_dequeue(void) +{ + struct rcu_head *node, *next; + +retry: + /* Test for an empty list, which we do not expect. Note that for + * the consumer head and tail are always consistent. The head + * is consistent because only the consumer reads/writes it. + * The tail, because it is the first step in the enqueuing. + * It is only the next pointers that might be inconsistent. + */ + if (head == &dummy && atomic_mb_read(&tail) == &dummy.next) { + abort(); + } + + /* If the head node has NULL in its next pointer, the value is + * wrong and we need to wait until its enqueuer finishes the update. + */ + node = head; + next = atomic_mb_read(&head->next); + if (!next) { + return NULL; + } + + /* Since we are the sole consumer, and we excluded the empty case + * above, the queue will always have at least two nodes: the + * dummy node, and the one being removed. So we do not need to update + * the tail pointer. + */ + head = next; + + /* If we dequeued the dummy node, add it back at the end and retry. */ + if (node == &dummy) { + enqueue(node); + goto retry; + } + + return node; +} + +static void *call_rcu_thread(void *opaque) +{ + struct rcu_head *node; + + rcu_register_thread(); + + for (;;) { + int tries = 0; + int n = atomic_read(&rcu_call_count); + + /* Heuristically wait for a decent number of callbacks to pile up. + * Fetch rcu_call_count now, we only must process elements that were + * added before synchronize_rcu() starts. + */ + while (n == 0 || (n < RCU_CALL_MIN_SIZE && ++tries <= 5)) { + g_usleep(10000); + if (n == 0) { + qemu_event_reset(&rcu_call_ready_event); + n = atomic_read(&rcu_call_count); + if (n == 0) { + qemu_event_wait(&rcu_call_ready_event); + } + } + n = atomic_read(&rcu_call_count); + } + + atomic_sub(&rcu_call_count, n); + synchronize_rcu(); + qemu_mutex_lock_iothread(); + while (n > 0) { + node = try_dequeue(); + while (!node) { + qemu_mutex_unlock_iothread(); + qemu_event_reset(&rcu_call_ready_event); + node = try_dequeue(); + if (!node) { + qemu_event_wait(&rcu_call_ready_event); + node = try_dequeue(); + } + qemu_mutex_lock_iothread(); + } + + n--; + node->func(node); + } + qemu_mutex_unlock_iothread(); + } + abort(); +} + +void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node)) +{ + node->func = func; + enqueue(node); + atomic_inc(&rcu_call_count); + qemu_event_set(&rcu_call_ready_event); +} + +void rcu_register_thread(void) +{ + assert(rcu_reader.ctr == 0); + qemu_mutex_lock(&rcu_gp_lock); + QLIST_INSERT_HEAD(®istry, &rcu_reader, node); + qemu_mutex_unlock(&rcu_gp_lock); +} + +void rcu_unregister_thread(void) +{ + qemu_mutex_lock(&rcu_gp_lock); + QLIST_REMOVE(&rcu_reader, node); + qemu_mutex_unlock(&rcu_gp_lock); +} + +static void rcu_init_complete(void) +{ + QemuThread thread; + + qemu_mutex_init(&rcu_gp_lock); + qemu_event_init(&rcu_gp_event, true); + + qemu_event_init(&rcu_call_ready_event, false); + + /* The caller is assumed to have iothread lock, so the call_rcu thread + * must have been quiescent even after forking, just recreate it. + */ + qemu_thread_create(&thread, "call_rcu", call_rcu_thread, + NULL, QEMU_THREAD_DETACHED); + + rcu_register_thread(); +} + +#ifdef CONFIG_POSIX +static void rcu_init_lock(void) +{ + qemu_mutex_lock(&rcu_gp_lock); +} + +static void rcu_init_unlock(void) +{ + qemu_mutex_unlock(&rcu_gp_lock); +} +#endif + +void rcu_after_fork(void) +{ + memset(®istry, 0, sizeof(registry)); + rcu_init_complete(); +} + +static void __attribute__((__constructor__)) rcu_init(void) +{ +#ifdef CONFIG_POSIX + pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_unlock); +#endif + rcu_init_complete(); +} -- cgit 1.2.3-korg