Merge remote-tracking branch 'remotes/dgilbert-gitlab/tags/pull-virtiofs-20210315...
[qemu/ar7.git] / util / thread-pool.c
blobd763cea505b68575af8e1b39cd95d02caa73801a
1 /*
2 * QEMU block layer thread pool
4 * Copyright IBM, Corp. 2008
5 * Copyright Red Hat, Inc. 2012
7 * Authors:
8 * Anthony Liguori <aliguori@us.ibm.com>
9 * Paolo Bonzini <pbonzini@redhat.com>
11 * This work is licensed under the terms of the GNU GPL, version 2. See
12 * the COPYING file in the top-level directory.
14 * Contributions after 2012-01-13 are licensed under the terms of the
15 * GNU GPL, version 2 or (at your option) any later version.
17 #include "qemu/osdep.h"
18 #include "qemu/queue.h"
19 #include "qemu/thread.h"
20 #include "qemu/coroutine.h"
21 #include "trace.h"
22 #include "block/thread-pool.h"
23 #include "qemu/main-loop.h"
25 static void do_spawn_thread(ThreadPool *pool);
27 typedef struct ThreadPoolElement ThreadPoolElement;
29 enum ThreadState {
30 THREAD_QUEUED,
31 THREAD_ACTIVE,
32 THREAD_DONE,
35 struct ThreadPoolElement {
36 BlockAIOCB common;
37 ThreadPool *pool;
38 ThreadPoolFunc *func;
39 void *arg;
41 /* Moving state out of THREAD_QUEUED is protected by lock. After
42 * that, only the worker thread can write to it. Reads and writes
43 * of state and ret are ordered with memory barriers.
45 enum ThreadState state;
46 int ret;
48 /* Access to this list is protected by lock. */
49 QTAILQ_ENTRY(ThreadPoolElement) reqs;
51 /* Access to this list is protected by the global mutex. */
52 QLIST_ENTRY(ThreadPoolElement) all;
55 struct ThreadPool {
56 AioContext *ctx;
57 QEMUBH *completion_bh;
58 QemuMutex lock;
59 QemuCond worker_stopped;
60 QemuSemaphore sem;
61 int max_threads;
62 QEMUBH *new_thread_bh;
64 /* The following variables are only accessed from one AioContext. */
65 QLIST_HEAD(, ThreadPoolElement) head;
67 /* The following variables are protected by lock. */
68 QTAILQ_HEAD(, ThreadPoolElement) request_list;
69 int cur_threads;
70 int idle_threads;
71 int new_threads; /* backlog of threads we need to create */
72 int pending_threads; /* threads created but not running yet */
73 bool stopping;
76 static void *worker_thread(void *opaque)
78 ThreadPool *pool = opaque;
80 qemu_mutex_lock(&pool->lock);
81 pool->pending_threads--;
82 do_spawn_thread(pool);
84 while (!pool->stopping) {
85 ThreadPoolElement *req;
86 int ret;
88 do {
89 pool->idle_threads++;
90 qemu_mutex_unlock(&pool->lock);
91 ret = qemu_sem_timedwait(&pool->sem, 10000);
92 qemu_mutex_lock(&pool->lock);
93 pool->idle_threads--;
94 } while (ret == -1 && !QTAILQ_EMPTY(&pool->request_list));
95 if (ret == -1 || pool->stopping) {
96 break;
99 req = QTAILQ_FIRST(&pool->request_list);
100 QTAILQ_REMOVE(&pool->request_list, req, reqs);
101 req->state = THREAD_ACTIVE;
102 qemu_mutex_unlock(&pool->lock);
104 ret = req->func(req->arg);
106 req->ret = ret;
107 /* Write ret before state. */
108 smp_wmb();
109 req->state = THREAD_DONE;
111 qemu_mutex_lock(&pool->lock);
113 qemu_bh_schedule(pool->completion_bh);
116 pool->cur_threads--;
117 qemu_cond_signal(&pool->worker_stopped);
118 qemu_mutex_unlock(&pool->lock);
119 return NULL;
122 static void do_spawn_thread(ThreadPool *pool)
124 QemuThread t;
126 /* Runs with lock taken. */
127 if (!pool->new_threads) {
128 return;
131 pool->new_threads--;
132 pool->pending_threads++;
134 qemu_thread_create(&t, "worker", worker_thread, pool, QEMU_THREAD_DETACHED);
137 static void spawn_thread_bh_fn(void *opaque)
139 ThreadPool *pool = opaque;
141 qemu_mutex_lock(&pool->lock);
142 do_spawn_thread(pool);
143 qemu_mutex_unlock(&pool->lock);
146 static void spawn_thread(ThreadPool *pool)
148 pool->cur_threads++;
149 pool->new_threads++;
150 /* If there are threads being created, they will spawn new workers, so
151 * we don't spend time creating many threads in a loop holding a mutex or
152 * starving the current vcpu.
154 * If there are no idle threads, ask the main thread to create one, so we
155 * inherit the correct affinity instead of the vcpu affinity.
157 if (!pool->pending_threads) {
158 qemu_bh_schedule(pool->new_thread_bh);
162 static void thread_pool_completion_bh(void *opaque)
164 ThreadPool *pool = opaque;
165 ThreadPoolElement *elem, *next;
167 aio_context_acquire(pool->ctx);
168 restart:
169 QLIST_FOREACH_SAFE(elem, &pool->head, all, next) {
170 if (elem->state != THREAD_DONE) {
171 continue;
174 trace_thread_pool_complete(pool, elem, elem->common.opaque,
175 elem->ret);
176 QLIST_REMOVE(elem, all);
178 if (elem->common.cb) {
179 /* Read state before ret. */
180 smp_rmb();
182 /* Schedule ourselves in case elem->common.cb() calls aio_poll() to
183 * wait for another request that completed at the same time.
185 qemu_bh_schedule(pool->completion_bh);
187 aio_context_release(pool->ctx);
188 elem->common.cb(elem->common.opaque, elem->ret);
189 aio_context_acquire(pool->ctx);
191 /* We can safely cancel the completion_bh here regardless of someone
192 * else having scheduled it meanwhile because we reenter the
193 * completion function anyway (goto restart).
195 qemu_bh_cancel(pool->completion_bh);
197 qemu_aio_unref(elem);
198 goto restart;
199 } else {
200 qemu_aio_unref(elem);
203 aio_context_release(pool->ctx);
206 static void thread_pool_cancel(BlockAIOCB *acb)
208 ThreadPoolElement *elem = (ThreadPoolElement *)acb;
209 ThreadPool *pool = elem->pool;
211 trace_thread_pool_cancel(elem, elem->common.opaque);
213 QEMU_LOCK_GUARD(&pool->lock);
214 if (elem->state == THREAD_QUEUED &&
215 /* No thread has yet started working on elem. we can try to "steal"
216 * the item from the worker if we can get a signal from the
217 * semaphore. Because this is non-blocking, we can do it with
218 * the lock taken and ensure that elem will remain THREAD_QUEUED.
220 qemu_sem_timedwait(&pool->sem, 0) == 0) {
221 QTAILQ_REMOVE(&pool->request_list, elem, reqs);
222 qemu_bh_schedule(pool->completion_bh);
224 elem->state = THREAD_DONE;
225 elem->ret = -ECANCELED;
230 static AioContext *thread_pool_get_aio_context(BlockAIOCB *acb)
232 ThreadPoolElement *elem = (ThreadPoolElement *)acb;
233 ThreadPool *pool = elem->pool;
234 return pool->ctx;
237 static const AIOCBInfo thread_pool_aiocb_info = {
238 .aiocb_size = sizeof(ThreadPoolElement),
239 .cancel_async = thread_pool_cancel,
240 .get_aio_context = thread_pool_get_aio_context,
243 BlockAIOCB *thread_pool_submit_aio(ThreadPool *pool,
244 ThreadPoolFunc *func, void *arg,
245 BlockCompletionFunc *cb, void *opaque)
247 ThreadPoolElement *req;
249 req = qemu_aio_get(&thread_pool_aiocb_info, NULL, cb, opaque);
250 req->func = func;
251 req->arg = arg;
252 req->state = THREAD_QUEUED;
253 req->pool = pool;
255 QLIST_INSERT_HEAD(&pool->head, req, all);
257 trace_thread_pool_submit(pool, req, arg);
259 qemu_mutex_lock(&pool->lock);
260 if (pool->idle_threads == 0 && pool->cur_threads < pool->max_threads) {
261 spawn_thread(pool);
263 QTAILQ_INSERT_TAIL(&pool->request_list, req, reqs);
264 qemu_mutex_unlock(&pool->lock);
265 qemu_sem_post(&pool->sem);
266 return &req->common;
269 typedef struct ThreadPoolCo {
270 Coroutine *co;
271 int ret;
272 } ThreadPoolCo;
274 static void thread_pool_co_cb(void *opaque, int ret)
276 ThreadPoolCo *co = opaque;
278 co->ret = ret;
279 aio_co_wake(co->co);
282 int coroutine_fn thread_pool_submit_co(ThreadPool *pool, ThreadPoolFunc *func,
283 void *arg)
285 ThreadPoolCo tpc = { .co = qemu_coroutine_self(), .ret = -EINPROGRESS };
286 assert(qemu_in_coroutine());
287 thread_pool_submit_aio(pool, func, arg, thread_pool_co_cb, &tpc);
288 qemu_coroutine_yield();
289 return tpc.ret;
292 void thread_pool_submit(ThreadPool *pool, ThreadPoolFunc *func, void *arg)
294 thread_pool_submit_aio(pool, func, arg, NULL, NULL);
297 static void thread_pool_init_one(ThreadPool *pool, AioContext *ctx)
299 if (!ctx) {
300 ctx = qemu_get_aio_context();
303 memset(pool, 0, sizeof(*pool));
304 pool->ctx = ctx;
305 pool->completion_bh = aio_bh_new(ctx, thread_pool_completion_bh, pool);
306 qemu_mutex_init(&pool->lock);
307 qemu_cond_init(&pool->worker_stopped);
308 qemu_sem_init(&pool->sem, 0);
309 pool->max_threads = 64;
310 pool->new_thread_bh = aio_bh_new(ctx, spawn_thread_bh_fn, pool);
312 QLIST_INIT(&pool->head);
313 QTAILQ_INIT(&pool->request_list);
316 ThreadPool *thread_pool_new(AioContext *ctx)
318 ThreadPool *pool = g_new(ThreadPool, 1);
319 thread_pool_init_one(pool, ctx);
320 return pool;
323 void thread_pool_free(ThreadPool *pool)
325 if (!pool) {
326 return;
329 assert(QLIST_EMPTY(&pool->head));
331 qemu_mutex_lock(&pool->lock);
333 /* Stop new threads from spawning */
334 qemu_bh_delete(pool->new_thread_bh);
335 pool->cur_threads -= pool->new_threads;
336 pool->new_threads = 0;
338 /* Wait for worker threads to terminate */
339 pool->stopping = true;
340 while (pool->cur_threads > 0) {
341 qemu_sem_post(&pool->sem);
342 qemu_cond_wait(&pool->worker_stopped, &pool->lock);
345 qemu_mutex_unlock(&pool->lock);
347 qemu_bh_delete(pool->completion_bh);
348 qemu_sem_destroy(&pool->sem);
349 qemu_cond_destroy(&pool->worker_stopped);
350 qemu_mutex_destroy(&pool->lock);
351 g_free(pool);