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