--- /dev/null
+/*
+ * QEMU block layer thread pool
+ *
+ * Copyright IBM, Corp. 2008
+ * Copyright Red Hat, Inc. 2012
+ *
+ * Authors:
+ * Anthony Liguori <aliguori@us.ibm.com>
+ * Paolo Bonzini <pbonzini@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ *
+ * Contributions after 2012-01-13 are licensed under the terms of the
+ * GNU GPL, version 2 or (at your option) any later version.
+ */
+#include "qemu-common.h"
+#include "qemu/queue.h"
+#include "qemu/thread.h"
+#include "qemu/osdep.h"
+#include "block/coroutine.h"
+#include "trace.h"
+#include "block/thread-pool.h"
+#include "qemu/main-loop.h"
+
+static void do_spawn_thread(ThreadPool *pool);
+
+typedef struct ThreadPoolElement ThreadPoolElement;
+
+enum ThreadState {
+ THREAD_QUEUED,
+ THREAD_ACTIVE,
+ THREAD_DONE,
+};
+
+struct ThreadPoolElement {
+ BlockAIOCB common;
+ ThreadPool *pool;
+ ThreadPoolFunc *func;
+ void *arg;
+
+ /* Moving state out of THREAD_QUEUED is protected by lock. After
+ * that, only the worker thread can write to it. Reads and writes
+ * of state and ret are ordered with memory barriers.
+ */
+ enum ThreadState state;
+ int ret;
+
+ /* Access to this list is protected by lock. */
+ QTAILQ_ENTRY(ThreadPoolElement) reqs;
+
+ /* Access to this list is protected by the global mutex. */
+ QLIST_ENTRY(ThreadPoolElement) all;
+};
+
+struct ThreadPool {
+ AioContext *ctx;
+ QEMUBH *completion_bh;
+ QemuMutex lock;
+ QemuCond worker_stopped;
+ QemuSemaphore sem;
+ int max_threads;
+ QEMUBH *new_thread_bh;
+
+ /* The following variables are only accessed from one AioContext. */
+ QLIST_HEAD(, ThreadPoolElement) head;
+
+ /* The following variables are protected by lock. */
+ QTAILQ_HEAD(, ThreadPoolElement) request_list;
+ int cur_threads;
+ int idle_threads;
+ int new_threads; /* backlog of threads we need to create */
+ int pending_threads; /* threads created but not running yet */
+ bool stopping;
+};
+
+static void *worker_thread(void *opaque)
+{
+ ThreadPool *pool = opaque;
+
+ qemu_mutex_lock(&pool->lock);
+ pool->pending_threads--;
+ do_spawn_thread(pool);
+
+ while (!pool->stopping) {
+ ThreadPoolElement *req;
+ int ret;
+
+ do {
+ pool->idle_threads++;
+ qemu_mutex_unlock(&pool->lock);
+ ret = qemu_sem_timedwait(&pool->sem, 10000);
+ qemu_mutex_lock(&pool->lock);
+ pool->idle_threads--;
+ } while (ret == -1 && !QTAILQ_EMPTY(&pool->request_list));
+ if (ret == -1 || pool->stopping) {
+ break;
+ }
+
+ req = QTAILQ_FIRST(&pool->request_list);
+ QTAILQ_REMOVE(&pool->request_list, req, reqs);
+ req->state = THREAD_ACTIVE;
+ qemu_mutex_unlock(&pool->lock);
+
+ ret = req->func(req->arg);
+
+ req->ret = ret;
+ /* Write ret before state. */
+ smp_wmb();
+ req->state = THREAD_DONE;
+
+ qemu_mutex_lock(&pool->lock);
+
+ qemu_bh_schedule(pool->completion_bh);
+ }
+
+ pool->cur_threads--;
+ qemu_cond_signal(&pool->worker_stopped);
+ qemu_mutex_unlock(&pool->lock);
+ return NULL;
+}
+
+static void do_spawn_thread(ThreadPool *pool)
+{
+ QemuThread t;
+
+ /* Runs with lock taken. */
+ if (!pool->new_threads) {
+ return;
+ }
+
+ pool->new_threads--;
+ pool->pending_threads++;
+
+ qemu_thread_create(&t, "worker", worker_thread, pool, QEMU_THREAD_DETACHED);
+}
+
+static void spawn_thread_bh_fn(void *opaque)
+{
+ ThreadPool *pool = opaque;
+
+ qemu_mutex_lock(&pool->lock);
+ do_spawn_thread(pool);
+ qemu_mutex_unlock(&pool->lock);
+}
+
+static void spawn_thread(ThreadPool *pool)
+{
+ pool->cur_threads++;
+ pool->new_threads++;
+ /* If there are threads being created, they will spawn new workers, so
+ * we don't spend time creating many threads in a loop holding a mutex or
+ * starving the current vcpu.
+ *
+ * If there are no idle threads, ask the main thread to create one, so we
+ * inherit the correct affinity instead of the vcpu affinity.
+ */
+ if (!pool->pending_threads) {
+ qemu_bh_schedule(pool->new_thread_bh);
+ }
+}
+
+static void thread_pool_completion_bh(void *opaque)
+{
+ ThreadPool *pool = opaque;
+ ThreadPoolElement *elem, *next;
+
+restart:
+ QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
+ if (elem->state != THREAD_DONE) {
+ continue;
+ }
+
+ trace_thread_pool_complete(pool, elem, elem->common.opaque,
+ elem->ret);
+ QLIST_REMOVE(elem, all);
+
+ if (elem->common.cb) {
+ /* Read state before ret. */
+ smp_rmb();
+
+ /* Schedule ourselves in case elem->common.cb() calls aio_poll() to
+ * wait for another request that completed at the same time.
+ */
+ qemu_bh_schedule(pool->completion_bh);
+
+ elem->common.cb(elem->common.opaque, elem->ret);
+ qemu_aio_unref(elem);
+ goto restart;
+ } else {
+ qemu_aio_unref(elem);
+ }
+ }
+}
+
+static void thread_pool_cancel(BlockAIOCB *acb)
+{
+ ThreadPoolElement *elem = (ThreadPoolElement *)acb;
+ ThreadPool *pool = elem->pool;
+
+ trace_thread_pool_cancel(elem, elem->common.opaque);
+
+ qemu_mutex_lock(&pool->lock);
+ if (elem->state == THREAD_QUEUED &&
+ /* No thread has yet started working on elem. we can try to "steal"
+ * the item from the worker if we can get a signal from the
+ * semaphore. Because this is non-blocking, we can do it with
+ * the lock taken and ensure that elem will remain THREAD_QUEUED.
+ */
+ qemu_sem_timedwait(&pool->sem, 0) == 0) {
+ QTAILQ_REMOVE(&pool->request_list, elem, reqs);
+ qemu_bh_schedule(pool->completion_bh);
+
+ elem->state = THREAD_DONE;
+ elem->ret = -ECANCELED;
+ }
+
+ qemu_mutex_unlock(&pool->lock);
+}
+
+static AioContext *thread_pool_get_aio_context(BlockAIOCB *acb)
+{
+ ThreadPoolElement *elem = (ThreadPoolElement *)acb;
+ ThreadPool *pool = elem->pool;
+ return pool->ctx;
+}
+
+static const AIOCBInfo thread_pool_aiocb_info = {
+ .aiocb_size = sizeof(ThreadPoolElement),
+ .cancel_async = thread_pool_cancel,
+ .get_aio_context = thread_pool_get_aio_context,
+};
+
+BlockAIOCB *thread_pool_submit_aio(ThreadPool *pool,
+ ThreadPoolFunc *func, void *arg,
+ BlockCompletionFunc *cb, void *opaque)
+{
+ ThreadPoolElement *req;
+
+ req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
+ req->func = func;
+ req->arg = arg;
+ req->state = THREAD_QUEUED;
+ req->pool = pool;
+
+ QLIST_INSERT_HEAD(&pool->head, req, all);
+
+ trace_thread_pool_submit(pool, req, arg);
+
+ qemu_mutex_lock(&pool->lock);
+ if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
+ spawn_thread(pool);
+ }
+ QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
+ qemu_mutex_unlock(&pool->lock);
+ qemu_sem_post(&pool->sem);
+ return &req->common;
+}
+
+typedef struct ThreadPoolCo {
+ Coroutine *co;
+ int ret;
+} ThreadPoolCo;
+
+static void thread_pool_co_cb(void *opaque, int ret)
+{
+ ThreadPoolCo *co = opaque;
+
+ co->ret = ret;
+ qemu_coroutine_enter(co->co, NULL);
+}
+
+int coroutine_fn thread_pool_submit_co(ThreadPool *pool, ThreadPoolFunc *func,
+ void *arg)
+{
+ ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
+ assert(qemu_in_coroutine());
+ thread_pool_submit_aio(pool, func, arg, thread_pool_co_cb, &tpc);
+ qemu_coroutine_yield();
+ return tpc.ret;
+}
+
+void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func, void *arg)
+{
+ thread_pool_submit_aio(pool, func, arg, NULL, NULL);
+}
+
+static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
+{
+ if (!ctx) {
+ ctx = qemu_get_aio_context();
+ }
+
+ memset(pool, 0, sizeof(*pool));
+ pool->ctx = ctx;
+ pool->completion_bh = aio_bh_new(ctx, thread_pool_completion_bh, pool);
+ qemu_mutex_init(&pool->lock);
+ qemu_cond_init(&pool->worker_stopped);
+ qemu_sem_init(&pool->sem, 0);
+ pool->max_threads = 64;
+ pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
+
+ QLIST_INIT(&pool->head);
+ QTAILQ_INIT(&pool->request_list);
+}
+
+ThreadPool *thread_pool_new(AioContext *ctx)
+{
+ ThreadPool *pool = g_new(ThreadPool, 1);
+ thread_pool_init_one(pool, ctx);
+ return pool;
+}
+
+void thread_pool_free(ThreadPool *pool)
+{
+ if (!pool) {
+ return;
+ }
+
+ assert(QLIST_EMPTY(&pool->head));
+
+ qemu_mutex_lock(&pool->lock);
+
+ /* Stop new threads from spawning */
+ qemu_bh_delete(pool->new_thread_bh);
+ pool->cur_threads -= pool->new_threads;
+ pool->new_threads = 0;
+
+ /* Wait for worker threads to terminate */
+ pool->stopping = true;
+ while (pool->cur_threads > 0) {
+ qemu_sem_post(&pool->sem);
+ qemu_cond_wait(&pool->worker_stopped, &pool->lock);
+ }
+
+ qemu_mutex_unlock(&pool->lock);
+
+ qemu_bh_delete(pool->completion_bh);
+ qemu_sem_destroy(&pool->sem);
+ qemu_cond_destroy(&pool->worker_stopped);
+ qemu_mutex_destroy(&pool->lock);
+ g_free(pool);
+}
Code Review / kvmfornfv.git / blobdiff