qemu

thread-pool.c (10637B)

---

 /*
  * 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/osdep.h"
 #include "qemu/queue.h"
 #include "qemu/thread.h"
 #include "qemu/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;
     QemuCond request_cond;
     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 */
     int min_threads;
     int max_threads;
 };
 
 static void *worker_thread(void *opaque)
 {
     ThreadPool *pool = opaque;
 
     qemu_mutex_lock(&pool->lock);
     pool->pending_threads--;
     do_spawn_thread(pool);
 
     while (pool->cur_threads <= pool->max_threads) {
         ThreadPoolElement *req;
         int ret;
 
         if (QTAILQ_EMPTY(&pool->request_list)) {
             pool->idle_threads++;
             ret = qemu_cond_timedwait(&pool->request_cond, &pool->lock, 10000);
             pool->idle_threads--;
             if (ret == 0 &&
                 QTAILQ_EMPTY(&pool->request_list) &&
                 pool->cur_threads > pool->min_threads) {
                 /* Timed out + no work to do + no need for warm threads = exit.  */
                 break;
             }
             /*
              * Even if there was some work to do, check if there aren't
              * too many worker threads before picking it up.
              */
             continue;
         }
 
         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_bh_schedule(pool->completion_bh);
         qemu_mutex_lock(&pool->lock);
     }
 
     pool->cur_threads--;
     qemu_cond_signal(&pool->worker_stopped);
     qemu_mutex_unlock(&pool->lock);
 
     /*
      * Wake up another thread, in case we got a wakeup but decided
      * to exit due to pool->cur_threads > pool->max_threads.
      */
     qemu_cond_signal(&pool->request_cond);
     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;
 
     aio_context_acquire(pool->ctx);
 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);
 
             aio_context_release(pool->ctx);
             elem->common.cb(elem->common.opaque, elem->ret);
             aio_context_acquire(pool->ctx);
 
             /* We can safely cancel the completion_bh here regardless of someone
              * else having scheduled it meanwhile because we reenter the
              * completion function anyway (goto restart).
              */
             qemu_bh_cancel(pool->completion_bh);
 
             qemu_aio_unref(elem);
             goto restart;
         } else {
             qemu_aio_unref(elem);
         }
     }
     aio_context_release(pool->ctx);
 }
 
 static void thread_pool_cancel(BlockAIOCB *acb)
 {
     ThreadPoolElement *elem = (ThreadPoolElement *)acb;
     ThreadPool *pool = elem->pool;
 
     trace_thread_pool_cancel(elem, elem->common.opaque);
 
     QEMU_LOCK_GUARD(&pool->lock);
     if (elem->state == THREAD_QUEUED) {
         QTAILQ_REMOVE(&pool->request_list, elem, reqs);
         qemu_bh_schedule(pool->completion_bh);
 
         elem->state = THREAD_DONE;
         elem->ret = -ECANCELED;
     }
 
 }
 
 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_cond_signal(&pool->request_cond);
     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;
     aio_co_wake(co->co);
 }
 
 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);
 }
 
 void thread_pool_update_params(ThreadPool *pool, AioContext *ctx)
 {
     qemu_mutex_lock(&pool->lock);
 
     pool->min_threads = ctx->thread_pool_min;
     pool->max_threads = ctx->thread_pool_max;
 
     /*
      * We either have to:
      *  - Increase the number available of threads until over the min_threads
      *    threshold.
      *  - Bump the worker threads so that they exit, until under the max_threads
      *    threshold.
      *  - Do nothing. The current number of threads fall in between the min and
      *    max thresholds. We'll let the pool manage itself.
      */
     for (int i = pool->cur_threads; i < pool->min_threads; i++) {
         spawn_thread(pool);
     }
 
     for (int i = pool->cur_threads; i > pool->max_threads; i--) {
         qemu_cond_signal(&pool->request_cond);
     }
 
     qemu_mutex_unlock(&pool->lock);
 }
 
 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_cond_init(&pool->request_cond);
     pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
 
     QLIST_INIT(&pool->head);
     QTAILQ_INIT(&pool->request_list);
 
     thread_pool_update_params(pool, ctx);
 }
 
 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->max_threads = 0;
     qemu_cond_broadcast(&pool->request_cond);
     while (pool->cur_threads > 0) {
         qemu_cond_wait(&pool->worker_stopped, &pool->lock);
     }
 
     qemu_mutex_unlock(&pool->lock);
 
     qemu_bh_delete(pool->completion_bh);
     qemu_cond_destroy(&pool->request_cond);
     qemu_cond_destroy(&pool->worker_stopped);
     qemu_mutex_destroy(&pool->lock);
     g_free(pool);
 }