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13652c4b MD |
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> | |
7a618cf7 | 27 | #include <urcu/lfstack.h> |
13652c4b MD |
28 | #include <urcu/waitqueue-lifo.h> |
29 | #include <urcu/wfcqueue.h> | |
30 | #include <urcu/rculist.h> | |
31 | #include <pthread.h> | |
e10c65b3 | 32 | #include <assert.h> |
13652c4b | 33 | |
1b0a9891 MD |
34 | enum urcu_accept_ret { |
35 | URCU_ACCEPT_WORK = 0, | |
36 | URCU_ACCEPT_SHUTDOWN = 1, | |
37 | }; | |
38 | ||
13652c4b MD |
39 | /* |
40 | * We use RCU to steal work from siblings. Therefore, one of RCU flavors | |
41 | * need to be included before this header. All worker that participate | |
42 | * in stealing (initialized with the URCU_WORKER_STEAL flag) need to be | |
43 | * registered RCU readers threads. | |
44 | */ | |
45 | ||
46 | struct urcu_work { | |
47 | struct cds_wfcq_node node; | |
48 | }; | |
49 | ||
50 | struct urcu_workqueue { | |
51 | /* FIFO work queue */ | |
52 | struct __cds_wfcq_head head; | |
53 | struct cds_wfcq_tail tail; | |
54 | ||
55 | /* Associated wait queue for LIFO wait/wakeup */ | |
56 | struct urcu_wait_queue waitqueue; | |
57 | ||
58 | /* RCU linked list head of siblings for work stealing. */ | |
59 | struct cds_list_head sibling_head; | |
60 | pthread_mutex_t sibling_lock; /* Protect sibling list updates */ | |
1b0a9891 MD |
61 | |
62 | bool shutdown; /* Shutdown performed */ | |
13652c4b MD |
63 | }; |
64 | ||
65 | struct urcu_worker { | |
66 | struct cds_wfcq_head head; | |
67 | struct cds_wfcq_tail tail; | |
68 | ||
69 | struct urcu_wait_node wait_node; | |
70 | /* RCU linked list node of siblings for work stealing. */ | |
71 | struct cds_list_head sibling_node; | |
72 | int flags; /* enum urcu_worker_flags */ | |
73 | }; | |
74 | ||
75 | enum urcu_worker_flags { | |
76 | URCU_WORKER_STEAL = (1 << 0), | |
77 | }; | |
78 | ||
79 | static inline | |
80 | void urcu_workqueue_init(struct urcu_workqueue *queue) | |
81 | { | |
82 | __cds_wfcq_init(&queue->head, &queue->tail); | |
83 | urcu_wait_queue_init(&queue->waitqueue); | |
84 | CDS_INIT_LIST_HEAD(&queue->sibling_head); | |
1b0a9891 | 85 | queue->shutdown = false; |
13652c4b MD |
86 | } |
87 | ||
88 | static inline | |
89 | void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work) | |
90 | { | |
91 | bool was_empty; | |
92 | ||
93 | cds_wfcq_node_init(&work->node); | |
94 | ||
95 | /* Enqueue work. */ | |
96 | was_empty = !cds_wfcq_enqueue(&queue->head, &queue->tail, | |
97 | &work->node); | |
98 | /* | |
99 | * If workqueue was previously empty, wakeup one worker thread. | |
100 | * It will eventually grab the entire content of the work-queue | |
101 | * (therefore grabbing a "work batch"). After having grabbed the | |
102 | * work batch, while that thread is running and taking care of | |
103 | * that work batch, when we enqueue more work, we will wake | |
104 | * another thread (if there is one waiting), which will | |
105 | * eventually grab the new batch, and so on. This scheme ensures | |
106 | * that contiguous batch of work are handled by the same thread | |
107 | * (for locality), and also ensures that we scale work to many | |
108 | * worker threads when threads are busy enough to still be | |
109 | * running when work is enqueued. | |
110 | */ | |
d3afe039 MD |
111 | if (was_empty) { |
112 | rcu_read_lock(); /* Protect stack dequeue */ | |
13652c4b | 113 | (void) urcu_dequeue_wake_single(&queue->waitqueue); |
d3afe039 MD |
114 | rcu_read_unlock(); /* Protect stack dequeue */ |
115 | } | |
13652c4b MD |
116 | } |
117 | ||
118 | static inline | |
1b0a9891 | 119 | void __urcu_workqueue_wakeup_all(struct urcu_workqueue *queue) |
13652c4b MD |
120 | { |
121 | struct urcu_waiters waiters; | |
122 | ||
d3afe039 | 123 | rcu_read_lock(); /* Protect stack dequeue */ |
13652c4b | 124 | urcu_move_waiters(&waiters, &queue->waitqueue); |
d3afe039 MD |
125 | rcu_read_unlock(); /* Protect stack dequeue */ |
126 | ||
13652c4b MD |
127 | (void) urcu_wake_all_waiters(&waiters); |
128 | } | |
129 | ||
130 | static inline | |
131 | void urcu_worker_init(struct urcu_worker *worker, int flags) | |
132 | { | |
133 | cds_wfcq_init(&worker->head, &worker->tail); | |
134 | worker->flags = flags; | |
135 | urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING); | |
136 | } | |
137 | ||
138 | static inline | |
139 | void urcu_worker_register(struct urcu_workqueue *queue, | |
140 | struct urcu_worker *worker) | |
141 | { | |
142 | if (worker->flags & URCU_WORKER_STEAL) { | |
143 | pthread_mutex_lock(&queue->sibling_lock); | |
144 | cds_list_add_rcu(&worker->sibling_node, &queue->sibling_head); | |
145 | pthread_mutex_unlock(&queue->sibling_lock); | |
146 | } | |
147 | } | |
148 | ||
149 | static inline | |
150 | void urcu_worker_unregister(struct urcu_workqueue *queue, | |
151 | struct urcu_worker *worker) | |
152 | { | |
153 | enum cds_wfcq_ret wfcq_ret; | |
154 | ||
155 | if (worker->flags & URCU_WORKER_STEAL) { | |
156 | pthread_mutex_lock(&queue->sibling_lock); | |
157 | cds_list_del_rcu(&worker->sibling_node); | |
158 | pthread_mutex_unlock(&queue->sibling_lock); | |
13652c4b MD |
159 | } |
160 | ||
d3afe039 MD |
161 | /* |
162 | * Wait for grace period before freeing or reusing | |
163 | * "worker" because used by RCU linked list. | |
164 | * Also prevents ABA for waitqueue stack dequeue: matches RCU | |
165 | * read-side critical sections around dequeue and move all | |
166 | * operations on waitqueue). | |
167 | */ | |
168 | synchronize_rcu(); | |
169 | ||
13652c4b MD |
170 | /* |
171 | * Put any local work we still have back into the workqueue. | |
172 | */ | |
173 | wfcq_ret = __cds_wfcq_splice_blocking(&queue->head, | |
174 | &queue->tail, | |
175 | &worker->head, | |
176 | &worker->tail); | |
177 | if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY | |
178 | && wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) { | |
179 | /* | |
180 | * Wakeup worker thread if we have put work back into | |
181 | * workqueue that was previously empty. | |
182 | */ | |
d3afe039 | 183 | rcu_read_lock(); /* Protect stack dequeue */ |
13652c4b | 184 | (void) urcu_dequeue_wake_single(&queue->waitqueue); |
d3afe039 | 185 | rcu_read_unlock(); /* Protect stack dequeue */ |
13652c4b MD |
186 | } |
187 | } | |
188 | ||
189 | /* | |
190 | * Try stealing work from siblings when we have nothing to do. | |
191 | */ | |
192 | static inline | |
e10c65b3 | 193 | bool ___urcu_steal_work(struct urcu_worker *worker, |
13652c4b MD |
194 | struct urcu_worker *sibling) |
195 | { | |
e10c65b3 MD |
196 | enum cds_wfcq_ret splice_ret; |
197 | ||
30926570 MD |
198 | /* |
199 | * Don't bother grabbing the sibling queue lock if it is empty. | |
200 | */ | |
201 | if (cds_wfcq_empty(&sibling->head, &sibling->tail)) | |
e10c65b3 | 202 | return false; |
0695bd20 | 203 | splice_ret = cds_wfcq_splice_blocking(&worker->head, |
13652c4b MD |
204 | &worker->tail, |
205 | &sibling->head, | |
206 | &sibling->tail); | |
e10c65b3 MD |
207 | /* Ensure that we preserve FIFO work order. */ |
208 | assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY); | |
209 | return splice_ret != CDS_WFCQ_RET_SRC_EMPTY; | |
13652c4b MD |
210 | } |
211 | ||
212 | static inline | |
e10c65b3 | 213 | bool __urcu_steal_work(struct urcu_workqueue *queue, |
13652c4b MD |
214 | struct urcu_worker *worker) |
215 | { | |
216 | struct urcu_worker *sibling_prev, *sibling_next; | |
217 | struct cds_list_head *sibling_node; | |
e10c65b3 | 218 | bool steal_performed = 0; |
13652c4b MD |
219 | |
220 | if (!(worker->flags & URCU_WORKER_STEAL)) | |
e10c65b3 | 221 | return false; |
13652c4b MD |
222 | |
223 | rcu_read_lock(); | |
224 | ||
225 | sibling_node = rcu_dereference(worker->sibling_node.next); | |
226 | if (sibling_node == &queue->sibling_head) | |
227 | sibling_node = rcu_dereference(sibling_node->next); | |
228 | sibling_next = caa_container_of(sibling_node, struct urcu_worker, | |
229 | sibling_node); | |
230 | if (sibling_next != worker) | |
e10c65b3 MD |
231 | steal_performed = ___urcu_steal_work(worker, sibling_next); |
232 | if (steal_performed) | |
233 | goto end; | |
13652c4b MD |
234 | |
235 | sibling_node = rcu_dereference(worker->sibling_node.prev); | |
236 | if (sibling_node == &queue->sibling_head) | |
237 | sibling_node = rcu_dereference(sibling_node->prev); | |
238 | sibling_prev = caa_container_of(sibling_node, struct urcu_worker, | |
239 | sibling_node); | |
240 | if (sibling_prev != worker && sibling_prev != sibling_next) | |
e10c65b3 MD |
241 | steal_performed = ___urcu_steal_work(worker, sibling_prev); |
242 | end: | |
13652c4b MD |
243 | rcu_read_unlock(); |
244 | ||
e10c65b3 | 245 | return steal_performed; |
13652c4b MD |
246 | } |
247 | ||
248 | static inline | |
5d30bf32 | 249 | bool ___urcu_wakeup_sibling(struct urcu_worker *sibling) |
13652c4b | 250 | { |
5d30bf32 | 251 | return urcu_adaptative_wake_up(&sibling->wait_node); |
13652c4b MD |
252 | } |
253 | ||
254 | static inline | |
5d30bf32 | 255 | bool __urcu_wakeup_siblings(struct urcu_workqueue *queue, |
13652c4b MD |
256 | struct urcu_worker *worker) |
257 | { | |
258 | struct urcu_worker *sibling_prev, *sibling_next; | |
259 | struct cds_list_head *sibling_node; | |
5d30bf32 | 260 | bool wakeup_performed = 0; |
13652c4b MD |
261 | |
262 | if (!(worker->flags & URCU_WORKER_STEAL)) | |
263 | return; | |
264 | ||
265 | /* Only wakeup siblings if we have work in our own queue. */ | |
266 | if (cds_wfcq_empty(&worker->head, &worker->tail)) | |
267 | return; | |
268 | ||
269 | rcu_read_lock(); | |
270 | ||
271 | sibling_node = rcu_dereference(worker->sibling_node.next); | |
272 | if (sibling_node == &queue->sibling_head) | |
273 | sibling_node = rcu_dereference(sibling_node->next); | |
274 | sibling_next = caa_container_of(sibling_node, struct urcu_worker, | |
275 | sibling_node); | |
276 | if (sibling_next != worker) | |
5d30bf32 MD |
277 | wakeup_performed = ___urcu_wakeup_sibling(sibling_next); |
278 | if (wakeup_performed) | |
279 | goto end; | |
13652c4b MD |
280 | |
281 | sibling_node = rcu_dereference(worker->sibling_node.prev); | |
282 | if (sibling_node == &queue->sibling_head) | |
283 | sibling_node = rcu_dereference(sibling_node->prev); | |
284 | sibling_prev = caa_container_of(sibling_node, struct urcu_worker, | |
285 | sibling_node); | |
286 | if (sibling_prev != worker && sibling_prev != sibling_next) | |
5d30bf32 MD |
287 | wakeup_performed = ___urcu_wakeup_sibling(sibling_prev); |
288 | end: | |
13652c4b | 289 | rcu_read_unlock(); |
5d30bf32 MD |
290 | |
291 | return wakeup_performed; | |
13652c4b MD |
292 | } |
293 | ||
294 | static inline | |
1b0a9891 MD |
295 | enum urcu_accept_ret urcu_accept_work(struct urcu_workqueue *queue, |
296 | struct urcu_worker *worker) | |
13652c4b MD |
297 | { |
298 | enum cds_wfcq_ret wfcq_ret; | |
299 | ||
300 | wfcq_ret = __cds_wfcq_splice_blocking(&worker->head, | |
301 | &worker->tail, | |
302 | &queue->head, | |
303 | &queue->tail); | |
304 | /* Don't wait if we have work to do. */ | |
305 | if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY | |
306 | || !cds_wfcq_empty(&worker->head, | |
307 | &worker->tail)) | |
308 | goto do_work; | |
309 | /* Try to steal work from sibling instead of blocking */ | |
310 | if (__urcu_steal_work(queue, worker)) | |
311 | goto do_work; | |
1b0a9891 MD |
312 | /* No more work to do, check shutdown state */ |
313 | if (CMM_LOAD_SHARED(queue->shutdown)) | |
314 | return URCU_ACCEPT_SHUTDOWN; | |
13652c4b MD |
315 | urcu_wait_set_state(&worker->wait_node, |
316 | URCU_WAIT_WAITING); | |
317 | if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) { | |
318 | int was_empty; | |
319 | ||
320 | /* | |
321 | * NULL next pointer. We are therefore not in | |
322 | * the queue. | |
323 | */ | |
7a618cf7 | 324 | cds_lfs_node_init(&worker->wait_node.node); |
d3afe039 MD |
325 | /* Protect stack dequeue against ABA */ |
326 | synchronize_rcu(); | |
13652c4b MD |
327 | was_empty = !urcu_wait_add(&queue->waitqueue, |
328 | &worker->wait_node); | |
329 | /* | |
330 | * If the wait queue was empty, it means we are the | |
331 | * first thread to be put back into an otherwise empty | |
332 | * wait queue. Re-check if work queue is empty after | |
333 | * adding ourself to wait queue, so we can wakeup the | |
334 | * top of wait queue since new work have appeared, and | |
335 | * work enqueuer may not have seen that it needed to do | |
336 | * a wake up. | |
337 | */ | |
338 | if (was_empty && !cds_wfcq_empty(&queue->head, | |
d3afe039 MD |
339 | &queue->tail)) { |
340 | rcu_read_lock(); /* Protect stack dequeue */ | |
13652c4b | 341 | (void) urcu_dequeue_wake_single(&queue->waitqueue); |
d3afe039 MD |
342 | rcu_read_unlock(); /* Protect stack dequeue */ |
343 | } | |
13652c4b MD |
344 | } else { |
345 | /* | |
346 | * Non-NULL next pointer. We are therefore in | |
347 | * the queue, or the dispatcher just removed us | |
348 | * from it (after we read the next pointer), and | |
349 | * is therefore awakening us. The state will | |
350 | * therefore have been changed from WAITING to | |
351 | * some other state, which will let the busy | |
352 | * wait pass through. | |
353 | */ | |
354 | } | |
355 | urcu_adaptative_busy_wait(&worker->wait_node); | |
356 | return; | |
357 | ||
358 | do_work: | |
359 | /* | |
360 | * We will be busy handling the work batch, awaken siblings so | |
361 | * they can steal from us. | |
362 | */ | |
5d30bf32 | 363 | (void) __urcu_wakeup_siblings(queue, worker); |
1b0a9891 | 364 | return URCU_ACCEPT_WORK; |
13652c4b MD |
365 | } |
366 | ||
367 | static inline | |
368 | struct urcu_work *urcu_dequeue_work(struct urcu_worker *worker) | |
369 | { | |
370 | struct cds_wfcq_node *node; | |
371 | ||
372 | /* | |
373 | * If we are registered for work stealing, we need to dequeue | |
374 | * safely against siblings. | |
375 | */ | |
30926570 MD |
376 | if (worker->flags & URCU_WORKER_STEAL) { |
377 | /* | |
378 | * Don't bother grabbing the worker queue lock if it is | |
379 | * empty. | |
380 | */ | |
381 | if (cds_wfcq_empty(&worker->head, &worker->tail)) | |
382 | return NULL; | |
13652c4b MD |
383 | node = cds_wfcq_dequeue_blocking(&worker->head, |
384 | &worker->tail); | |
30926570 | 385 | } else { |
13652c4b MD |
386 | node = ___cds_wfcq_dequeue_with_state(&worker->head, |
387 | &worker->tail, NULL, 1, 0); | |
30926570 | 388 | } |
13652c4b MD |
389 | if (!node) |
390 | return NULL; | |
391 | return caa_container_of(node, struct urcu_work, node); | |
392 | } | |
393 | ||
1b0a9891 MD |
394 | static inline |
395 | void urcu_workqueue_shutdown(struct urcu_workqueue *queue) | |
396 | { | |
397 | /* Set shutdown */ | |
398 | CMM_STORE_SHARED(queue->shutdown, true); | |
399 | /* Wakeup all workers */ | |
400 | __urcu_workqueue_wakeup_all(queue); | |
401 | } | |
402 | ||
13652c4b | 403 | #endif /* _URCU_WORKQUEUE_FIFO_H */ |