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1 | #ifndef _URCU_WORKQUEUE_FIFO_H |
2 | #define _URCU_WORKQUEUE_FIFO_H | |
3 | ||
4 | /* | |
5 | * urcu/workqueue-fifo.h | |
6 | * | |
7 | * Userspace RCU library - work queue scheme with FIFO semantic | |
8 | * | |
9 | * Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
10 | * | |
11 | * This library is free software; you can redistribute it and/or | |
12 | * modify it under the terms of the GNU Lesser General Public | |
13 | * License as published by the Free Software Foundation; either | |
14 | * version 2.1 of the License, or (at your option) any later version. | |
15 | * | |
16 | * This library is distributed in the hope that it will be useful, | |
17 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
18 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
19 | * Lesser General Public License for more details. | |
20 | * | |
21 | * You should have received a copy of the GNU Lesser General Public | |
22 | * License along with this library; if not, write to the Free Software | |
23 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
24 | */ | |
25 | ||
26 | #include <urcu/uatomic.h> | |
27 | #include <urcu/wfstack.h> | |
28 | #include <urcu/waitqueue-lifo.h> | |
29 | #include <urcu/wfcqueue.h> | |
30 | #include <urcu/rculist.h> | |
31 | #include <pthread.h> | |
32 | ||
33 | /* | |
34 | * We use RCU to steal work from siblings. Therefore, one of RCU flavors | |
35 | * need to be included before this header. All worker that participate | |
36 | * in stealing (initialized with the URCU_WORKER_STEAL flag) need to be | |
37 | * registered RCU readers threads. | |
38 | */ | |
39 | ||
40 | struct urcu_work { | |
41 | struct cds_wfcq_node node; | |
42 | }; | |
43 | ||
44 | struct urcu_workqueue { | |
45 | /* FIFO work queue */ | |
46 | struct __cds_wfcq_head head; | |
47 | struct cds_wfcq_tail tail; | |
48 | ||
49 | /* Associated wait queue for LIFO wait/wakeup */ | |
50 | struct urcu_wait_queue waitqueue; | |
51 | ||
52 | /* RCU linked list head of siblings for work stealing. */ | |
53 | struct cds_list_head sibling_head; | |
54 | pthread_mutex_t sibling_lock; /* Protect sibling list updates */ | |
55 | }; | |
56 | ||
57 | struct urcu_worker { | |
58 | struct cds_wfcq_head head; | |
59 | struct cds_wfcq_tail tail; | |
60 | ||
61 | struct urcu_wait_node wait_node; | |
62 | /* RCU linked list node of siblings for work stealing. */ | |
63 | struct cds_list_head sibling_node; | |
64 | int flags; /* enum urcu_worker_flags */ | |
65 | }; | |
66 | ||
67 | enum urcu_worker_flags { | |
68 | URCU_WORKER_STEAL = (1 << 0), | |
69 | }; | |
70 | ||
71 | static inline | |
72 | void urcu_workqueue_init(struct urcu_workqueue *queue) | |
73 | { | |
74 | __cds_wfcq_init(&queue->head, &queue->tail); | |
75 | urcu_wait_queue_init(&queue->waitqueue); | |
76 | CDS_INIT_LIST_HEAD(&queue->sibling_head); | |
77 | } | |
78 | ||
79 | static inline | |
80 | void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work) | |
81 | { | |
82 | bool was_empty; | |
83 | ||
84 | cds_wfcq_node_init(&work->node); | |
85 | ||
86 | /* Enqueue work. */ | |
87 | was_empty = !cds_wfcq_enqueue(&queue->head, &queue->tail, | |
88 | &work->node); | |
89 | /* | |
90 | * If workqueue was previously empty, wakeup one worker thread. | |
91 | * It will eventually grab the entire content of the work-queue | |
92 | * (therefore grabbing a "work batch"). After having grabbed the | |
93 | * work batch, while that thread is running and taking care of | |
94 | * that work batch, when we enqueue more work, we will wake | |
95 | * another thread (if there is one waiting), which will | |
96 | * eventually grab the new batch, and so on. This scheme ensures | |
97 | * that contiguous batch of work are handled by the same thread | |
98 | * (for locality), and also ensures that we scale work to many | |
99 | * worker threads when threads are busy enough to still be | |
100 | * running when work is enqueued. | |
101 | */ | |
102 | if (was_empty) | |
103 | (void) urcu_dequeue_wake_single(&queue->waitqueue); | |
104 | } | |
105 | ||
106 | static inline | |
107 | void urcu_workqueue_wakeup_all(struct urcu_workqueue *queue) | |
108 | { | |
109 | struct urcu_waiters waiters; | |
110 | ||
111 | urcu_move_waiters(&waiters, &queue->waitqueue); | |
112 | (void) urcu_wake_all_waiters(&waiters); | |
113 | } | |
114 | ||
115 | static inline | |
116 | void urcu_worker_init(struct urcu_worker *worker, int flags) | |
117 | { | |
118 | cds_wfcq_init(&worker->head, &worker->tail); | |
119 | worker->flags = flags; | |
120 | urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING); | |
121 | } | |
122 | ||
123 | static inline | |
124 | void urcu_worker_register(struct urcu_workqueue *queue, | |
125 | struct urcu_worker *worker) | |
126 | { | |
127 | if (worker->flags & URCU_WORKER_STEAL) { | |
128 | pthread_mutex_lock(&queue->sibling_lock); | |
129 | cds_list_add_rcu(&worker->sibling_node, &queue->sibling_head); | |
130 | pthread_mutex_unlock(&queue->sibling_lock); | |
131 | } | |
132 | } | |
133 | ||
134 | static inline | |
135 | void urcu_worker_unregister(struct urcu_workqueue *queue, | |
136 | struct urcu_worker *worker) | |
137 | { | |
138 | enum cds_wfcq_ret wfcq_ret; | |
139 | ||
140 | if (worker->flags & URCU_WORKER_STEAL) { | |
141 | pthread_mutex_lock(&queue->sibling_lock); | |
142 | cds_list_del_rcu(&worker->sibling_node); | |
143 | pthread_mutex_unlock(&queue->sibling_lock); | |
144 | ||
145 | /* | |
146 | * Wait for grace period before freeing or reusing | |
147 | * "worker" because used by RCU linked list. | |
148 | */ | |
149 | synchronize_rcu(); | |
150 | } | |
151 | ||
152 | /* | |
153 | * Put any local work we still have back into the workqueue. | |
154 | */ | |
155 | wfcq_ret = __cds_wfcq_splice_blocking(&queue->head, | |
156 | &queue->tail, | |
157 | &worker->head, | |
158 | &worker->tail); | |
159 | if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY | |
160 | && wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) { | |
161 | /* | |
162 | * Wakeup worker thread if we have put work back into | |
163 | * workqueue that was previously empty. | |
164 | */ | |
165 | (void) urcu_dequeue_wake_single(&queue->waitqueue); | |
166 | } | |
167 | } | |
168 | ||
169 | /* | |
170 | * Try stealing work from siblings when we have nothing to do. | |
171 | */ | |
172 | static inline | |
173 | void ___urcu_steal_work(struct urcu_worker *worker, | |
174 | struct urcu_worker *sibling) | |
175 | { | |
176 | cds_wfcq_dequeue_lock(&sibling->head, &sibling->tail); | |
177 | (void) __cds_wfcq_splice_blocking(&worker->head, | |
178 | &worker->tail, | |
179 | &sibling->head, | |
180 | &sibling->tail); | |
181 | cds_wfcq_dequeue_unlock(&sibling->head, &sibling->tail); | |
182 | } | |
183 | ||
184 | static inline | |
185 | int __urcu_steal_work(struct urcu_workqueue *queue, | |
186 | struct urcu_worker *worker) | |
187 | { | |
188 | struct urcu_worker *sibling_prev, *sibling_next; | |
189 | struct cds_list_head *sibling_node; | |
190 | ||
191 | if (!(worker->flags & URCU_WORKER_STEAL)) | |
192 | return 0; | |
193 | ||
194 | rcu_read_lock(); | |
195 | ||
196 | sibling_node = rcu_dereference(worker->sibling_node.next); | |
197 | if (sibling_node == &queue->sibling_head) | |
198 | sibling_node = rcu_dereference(sibling_node->next); | |
199 | sibling_next = caa_container_of(sibling_node, struct urcu_worker, | |
200 | sibling_node); | |
201 | if (sibling_next != worker) | |
202 | ___urcu_steal_work(worker, sibling_next); | |
203 | ||
204 | sibling_node = rcu_dereference(worker->sibling_node.prev); | |
205 | if (sibling_node == &queue->sibling_head) | |
206 | sibling_node = rcu_dereference(sibling_node->prev); | |
207 | sibling_prev = caa_container_of(sibling_node, struct urcu_worker, | |
208 | sibling_node); | |
209 | if (sibling_prev != worker && sibling_prev != sibling_next) | |
210 | ___urcu_steal_work(worker, sibling_prev); | |
211 | ||
212 | rcu_read_unlock(); | |
213 | ||
214 | return !cds_wfcq_empty(&worker->head, &worker->tail); | |
215 | } | |
216 | ||
217 | static inline | |
218 | void ___urcu_wakeup_sibling(struct urcu_worker *sibling) | |
219 | { | |
220 | urcu_adaptative_wake_up(&sibling->wait_node); | |
221 | } | |
222 | ||
223 | static inline | |
224 | void __urcu_wakeup_siblings(struct urcu_workqueue *queue, | |
225 | struct urcu_worker *worker) | |
226 | { | |
227 | struct urcu_worker *sibling_prev, *sibling_next; | |
228 | struct cds_list_head *sibling_node; | |
229 | ||
230 | if (!(worker->flags & URCU_WORKER_STEAL)) | |
231 | return; | |
232 | ||
233 | /* Only wakeup siblings if we have work in our own queue. */ | |
234 | if (cds_wfcq_empty(&worker->head, &worker->tail)) | |
235 | return; | |
236 | ||
237 | rcu_read_lock(); | |
238 | ||
239 | sibling_node = rcu_dereference(worker->sibling_node.next); | |
240 | if (sibling_node == &queue->sibling_head) | |
241 | sibling_node = rcu_dereference(sibling_node->next); | |
242 | sibling_next = caa_container_of(sibling_node, struct urcu_worker, | |
243 | sibling_node); | |
244 | if (sibling_next != worker) | |
245 | ___urcu_wakeup_sibling(sibling_next); | |
246 | ||
247 | sibling_node = rcu_dereference(worker->sibling_node.prev); | |
248 | if (sibling_node == &queue->sibling_head) | |
249 | sibling_node = rcu_dereference(sibling_node->prev); | |
250 | sibling_prev = caa_container_of(sibling_node, struct urcu_worker, | |
251 | sibling_node); | |
252 | if (sibling_prev != worker && sibling_prev != sibling_next) | |
253 | ___urcu_wakeup_sibling(sibling_prev); | |
254 | ||
255 | rcu_read_unlock(); | |
256 | } | |
257 | ||
258 | static inline | |
259 | void urcu_accept_work(struct urcu_workqueue *queue, | |
260 | struct urcu_worker *worker, | |
261 | int blocking) | |
262 | { | |
263 | enum cds_wfcq_ret wfcq_ret; | |
264 | ||
265 | wfcq_ret = __cds_wfcq_splice_blocking(&worker->head, | |
266 | &worker->tail, | |
267 | &queue->head, | |
268 | &queue->tail); | |
269 | /* Don't wait if we have work to do. */ | |
270 | if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY | |
271 | || !cds_wfcq_empty(&worker->head, | |
272 | &worker->tail)) | |
273 | goto do_work; | |
274 | /* Try to steal work from sibling instead of blocking */ | |
275 | if (__urcu_steal_work(queue, worker)) | |
276 | goto do_work; | |
277 | if (!blocking) | |
278 | return; | |
279 | urcu_wait_set_state(&worker->wait_node, | |
280 | URCU_WAIT_WAITING); | |
281 | if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) { | |
282 | int was_empty; | |
283 | ||
284 | /* | |
285 | * NULL next pointer. We are therefore not in | |
286 | * the queue. | |
287 | */ | |
288 | cds_wfs_node_init(&worker->wait_node.node); | |
289 | was_empty = !urcu_wait_add(&queue->waitqueue, | |
290 | &worker->wait_node); | |
291 | /* | |
292 | * If the wait queue was empty, it means we are the | |
293 | * first thread to be put back into an otherwise empty | |
294 | * wait queue. Re-check if work queue is empty after | |
295 | * adding ourself to wait queue, so we can wakeup the | |
296 | * top of wait queue since new work have appeared, and | |
297 | * work enqueuer may not have seen that it needed to do | |
298 | * a wake up. | |
299 | */ | |
300 | if (was_empty && !cds_wfcq_empty(&queue->head, | |
301 | &queue->tail)) | |
302 | (void) urcu_dequeue_wake_single(&queue->waitqueue); | |
303 | } else { | |
304 | /* | |
305 | * Non-NULL next pointer. We are therefore in | |
306 | * the queue, or the dispatcher just removed us | |
307 | * from it (after we read the next pointer), and | |
308 | * is therefore awakening us. The state will | |
309 | * therefore have been changed from WAITING to | |
310 | * some other state, which will let the busy | |
311 | * wait pass through. | |
312 | */ | |
313 | } | |
314 | urcu_adaptative_busy_wait(&worker->wait_node); | |
315 | return; | |
316 | ||
317 | do_work: | |
318 | /* | |
319 | * We will be busy handling the work batch, awaken siblings so | |
320 | * they can steal from us. | |
321 | */ | |
322 | __urcu_wakeup_siblings(queue, worker); | |
323 | } | |
324 | ||
325 | static inline | |
326 | struct urcu_work *urcu_dequeue_work(struct urcu_worker *worker) | |
327 | { | |
328 | struct cds_wfcq_node *node; | |
329 | ||
330 | /* | |
331 | * If we are registered for work stealing, we need to dequeue | |
332 | * safely against siblings. | |
333 | */ | |
334 | if (worker->flags & URCU_WORKER_STEAL) | |
335 | node = cds_wfcq_dequeue_blocking(&worker->head, | |
336 | &worker->tail); | |
337 | else | |
338 | node = ___cds_wfcq_dequeue_with_state(&worker->head, | |
339 | &worker->tail, NULL, 1, 0); | |
340 | if (!node) | |
341 | return NULL; | |
342 | return caa_container_of(node, struct urcu_work, node); | |
343 | } | |
344 | ||
345 | #endif /* _URCU_WORKQUEUE_FIFO_H */ |