4 * Userspace RCU library - Userspace workqeues
6 * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
7 * Copyright (c) 2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
9 * This library is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this library; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
38 #include "compat-getcpu.h"
39 #include <urcu/wfcqueue.h>
40 #include <urcu/pointer.h>
41 #include <urcu/list.h>
42 #include <urcu/futex.h>
43 #include <urcu/tls-compat.h>
47 #include "workqueue.h"
49 #define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */
50 #define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1)
52 /* Data structure that identifies a workqueue. */
54 struct urcu_workqueue
{
56 * We do not align head on a different cache-line than tail
57 * mainly because workqueue threads use batching ("splice") to
58 * get an entire list of callbacks, which effectively empties
59 * the queue, and requires to touch the tail anyway.
61 struct cds_wfcq_tail cbs_tail
;
62 struct cds_wfcq_head cbs_head
;
65 unsigned long qlen
; /* maintained for debugging. */
68 unsigned long loop_count
;
70 void (*grace_period_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
71 void (*initialize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
72 void (*finalize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
73 void (*worker_before_pause_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
74 void (*worker_after_resume_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
75 void (*worker_before_wait_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
76 void (*worker_after_wake_up_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
77 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
79 struct urcu_workqueue_completion
{
85 struct urcu_workqueue_completion_work
{
86 struct urcu_work work
;
87 struct urcu_workqueue_completion
*completion
;
91 * Periodically retry setting CPU affinity if we migrate.
92 * Losing affinity can be caused by CPU hotunplug/hotplug, or by
95 #ifdef HAVE_SCHED_SETAFFINITY
96 static int set_thread_cpu_affinity(struct urcu_workqueue
*workqueue
)
101 if (workqueue
->cpu_affinity
< 0)
103 if (++workqueue
->loop_count
& SET_AFFINITY_CHECK_PERIOD_MASK
)
105 if (urcu_sched_getcpu() == workqueue
->cpu_affinity
)
109 CPU_SET(workqueue
->cpu_affinity
, &mask
);
110 #if SCHED_SETAFFINITY_ARGS == 2
111 ret
= sched_setaffinity(0, &mask
);
113 ret
= sched_setaffinity(0, sizeof(mask
), &mask
);
116 * EINVAL is fine: can be caused by hotunplugged CPUs, or by
117 * cpuset(7). This is why we should always retry if we detect
120 if (ret
&& errno
== EINVAL
) {
127 static int set_thread_cpu_affinity(struct urcu_workqueue
*workqueue
__attribute__((unused
)))
133 static void futex_wait(int32_t *futex
)
135 /* Read condition before read futex */
137 while (uatomic_read(futex
) == -1) {
138 if (!futex_async(futex
, FUTEX_WAIT
, -1, NULL
, NULL
, 0)) {
140 * Prior queued wakeups queued by unrelated code
141 * using the same address can cause futex wait to
142 * return 0 even through the futex value is still
143 * -1 (spurious wakeups). Check the value again
144 * in user-space to validate whether it really
151 /* Value already changed. */
154 /* Retry if interrupted by signal. */
155 break; /* Get out of switch. Check again. */
157 /* Unexpected error. */
163 static void futex_wake_up(int32_t *futex
)
165 /* Write to condition before reading/writing futex */
167 if (caa_unlikely(uatomic_read(futex
) == -1)) {
168 uatomic_set(futex
, 0);
169 if (futex_async(futex
, FUTEX_WAKE
, 1,
175 /* This is the code run by each worker thread. */
177 static void *workqueue_thread(void *arg
)
179 unsigned long cbcount
;
180 struct urcu_workqueue
*workqueue
= (struct urcu_workqueue
*) arg
;
181 int rt
= !!(uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_RT
);
183 if (set_thread_cpu_affinity(workqueue
))
186 if (workqueue
->initialize_worker_fct
)
187 workqueue
->initialize_worker_fct(workqueue
, workqueue
->priv
);
190 uatomic_dec(&workqueue
->futex
);
191 /* Decrement futex before reading workqueue */
195 struct cds_wfcq_head cbs_tmp_head
;
196 struct cds_wfcq_tail cbs_tmp_tail
;
197 struct cds_wfcq_node
*cbs
, *cbs_tmp_n
;
198 enum cds_wfcq_ret splice_ret
;
200 if (set_thread_cpu_affinity(workqueue
))
203 if (uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSE
) {
205 * Pause requested. Become quiescent: remove
206 * ourself from all global lists, and don't
207 * process any callback. The callback lists may
208 * still be non-empty though.
210 if (workqueue
->worker_before_pause_fct
)
211 workqueue
->worker_before_pause_fct(workqueue
, workqueue
->priv
);
212 cmm_smp_mb__before_uatomic_or();
213 uatomic_or(&workqueue
->flags
, URCU_WORKQUEUE_PAUSED
);
214 while ((uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSE
) != 0)
215 (void) poll(NULL
, 0, 1);
216 uatomic_and(&workqueue
->flags
, ~URCU_WORKQUEUE_PAUSED
);
217 cmm_smp_mb__after_uatomic_and();
218 if (workqueue
->worker_after_resume_fct
)
219 workqueue
->worker_after_resume_fct(workqueue
, workqueue
->priv
);
222 cds_wfcq_init(&cbs_tmp_head
, &cbs_tmp_tail
);
223 splice_ret
= __cds_wfcq_splice_blocking(&cbs_tmp_head
,
224 &cbs_tmp_tail
, &workqueue
->cbs_head
, &workqueue
->cbs_tail
);
225 assert(splice_ret
!= CDS_WFCQ_RET_WOULDBLOCK
);
226 assert(splice_ret
!= CDS_WFCQ_RET_DEST_NON_EMPTY
);
227 if (splice_ret
!= CDS_WFCQ_RET_SRC_EMPTY
) {
228 if (workqueue
->grace_period_fct
)
229 workqueue
->grace_period_fct(workqueue
, workqueue
->priv
);
231 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head
,
232 &cbs_tmp_tail
, cbs
, cbs_tmp_n
) {
233 struct urcu_work
*uwp
;
235 uwp
= caa_container_of(cbs
,
236 struct urcu_work
, next
);
240 uatomic_sub(&workqueue
->qlen
, cbcount
);
242 if (uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_STOP
)
244 if (workqueue
->worker_before_wait_fct
)
245 workqueue
->worker_before_wait_fct(workqueue
, workqueue
->priv
);
247 if (cds_wfcq_empty(&workqueue
->cbs_head
,
248 &workqueue
->cbs_tail
)) {
249 futex_wait(&workqueue
->futex
);
250 uatomic_dec(&workqueue
->futex
);
252 * Decrement futex before reading
258 if (cds_wfcq_empty(&workqueue
->cbs_head
,
259 &workqueue
->cbs_tail
)) {
260 (void) poll(NULL
, 0, 10);
263 if (workqueue
->worker_after_wake_up_fct
)
264 workqueue
->worker_after_wake_up_fct(workqueue
, workqueue
->priv
);
268 * Read urcu_work list before write futex.
271 uatomic_set(&workqueue
->futex
, 0);
273 if (workqueue
->finalize_worker_fct
)
274 workqueue
->finalize_worker_fct(workqueue
, workqueue
->priv
);
278 struct urcu_workqueue
*urcu_workqueue_create(unsigned long flags
,
279 int cpu_affinity
, void *priv
,
280 void (*grace_period_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
281 void (*initialize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
282 void (*finalize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
283 void (*worker_before_wait_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
284 void (*worker_after_wake_up_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
285 void (*worker_before_pause_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
286 void (*worker_after_resume_fct
)(struct urcu_workqueue
*workqueue
, void *priv
))
288 struct urcu_workqueue
*workqueue
;
291 workqueue
= malloc(sizeof(*workqueue
));
292 if (workqueue
== NULL
)
294 memset(workqueue
, '\0', sizeof(*workqueue
));
295 cds_wfcq_init(&workqueue
->cbs_head
, &workqueue
->cbs_tail
);
297 workqueue
->futex
= 0;
298 workqueue
->flags
= flags
;
299 workqueue
->priv
= priv
;
300 workqueue
->grace_period_fct
= grace_period_fct
;
301 workqueue
->initialize_worker_fct
= initialize_worker_fct
;
302 workqueue
->finalize_worker_fct
= finalize_worker_fct
;
303 workqueue
->worker_before_wait_fct
= worker_before_wait_fct
;
304 workqueue
->worker_after_wake_up_fct
= worker_after_wake_up_fct
;
305 workqueue
->worker_before_pause_fct
= worker_before_pause_fct
;
306 workqueue
->worker_after_resume_fct
= worker_after_resume_fct
;
307 workqueue
->cpu_affinity
= cpu_affinity
;
308 workqueue
->loop_count
= 0;
309 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
310 ret
= pthread_create(&workqueue
->tid
, NULL
, workqueue_thread
, workqueue
);
317 static void wake_worker_thread(struct urcu_workqueue
*workqueue
)
319 if (!(_CMM_LOAD_SHARED(workqueue
->flags
) & URCU_WORKQUEUE_RT
))
320 futex_wake_up(&workqueue
->futex
);
323 static int urcu_workqueue_destroy_worker(struct urcu_workqueue
*workqueue
)
328 uatomic_or(&workqueue
->flags
, URCU_WORKQUEUE_STOP
);
329 wake_worker_thread(workqueue
);
331 ret
= pthread_join(workqueue
->tid
, &retval
);
335 if (retval
!= NULL
) {
338 workqueue
->flags
&= ~URCU_WORKQUEUE_STOP
;
343 void urcu_workqueue_destroy(struct urcu_workqueue
*workqueue
)
345 if (workqueue
== NULL
) {
348 if (urcu_workqueue_destroy_worker(workqueue
)) {
351 assert(cds_wfcq_empty(&workqueue
->cbs_head
, &workqueue
->cbs_tail
));
355 void urcu_workqueue_queue_work(struct urcu_workqueue
*workqueue
,
356 struct urcu_work
*work
,
357 void (*func
)(struct urcu_work
*work
))
359 cds_wfcq_node_init(&work
->next
);
361 cds_wfcq_enqueue(&workqueue
->cbs_head
, &workqueue
->cbs_tail
, &work
->next
);
362 uatomic_inc(&workqueue
->qlen
);
363 wake_worker_thread(workqueue
);
367 void free_completion(struct urcu_ref
*ref
)
369 struct urcu_workqueue_completion
*completion
;
371 completion
= caa_container_of(ref
, struct urcu_workqueue_completion
, ref
);
376 void _urcu_workqueue_wait_complete(struct urcu_work
*work
)
378 struct urcu_workqueue_completion_work
*completion_work
;
379 struct urcu_workqueue_completion
*completion
;
381 completion_work
= caa_container_of(work
, struct urcu_workqueue_completion_work
, work
);
382 completion
= completion_work
->completion
;
383 if (!uatomic_sub_return(&completion
->barrier_count
, 1))
384 futex_wake_up(&completion
->futex
);
385 urcu_ref_put(&completion
->ref
, free_completion
);
386 free(completion_work
);
389 struct urcu_workqueue_completion
*urcu_workqueue_create_completion(void)
391 struct urcu_workqueue_completion
*completion
;
393 completion
= calloc(sizeof(*completion
), 1);
396 urcu_ref_set(&completion
->ref
, 1);
397 completion
->barrier_count
= 0;
401 void urcu_workqueue_destroy_completion(struct urcu_workqueue_completion
*completion
)
403 urcu_ref_put(&completion
->ref
, free_completion
);
406 void urcu_workqueue_wait_completion(struct urcu_workqueue_completion
*completion
)
410 uatomic_dec(&completion
->futex
);
411 /* Decrement futex before reading barrier_count */
413 if (!uatomic_read(&completion
->barrier_count
))
415 futex_wait(&completion
->futex
);
419 void urcu_workqueue_queue_completion(struct urcu_workqueue
*workqueue
,
420 struct urcu_workqueue_completion
*completion
)
422 struct urcu_workqueue_completion_work
*work
;
424 work
= calloc(sizeof(*work
), 1);
427 work
->completion
= completion
;
428 urcu_ref_get(&completion
->ref
);
429 uatomic_inc(&completion
->barrier_count
);
430 urcu_workqueue_queue_work(workqueue
, &work
->work
, _urcu_workqueue_wait_complete
);
434 * Wait for all in-flight work to complete execution.
436 void urcu_workqueue_flush_queued_work(struct urcu_workqueue
*workqueue
)
438 struct urcu_workqueue_completion
*completion
;
440 completion
= urcu_workqueue_create_completion();
443 urcu_workqueue_queue_completion(workqueue
, completion
);
444 urcu_workqueue_wait_completion(completion
);
445 urcu_workqueue_destroy_completion(completion
);
448 /* To be used in before fork handler. */
449 void urcu_workqueue_pause_worker(struct urcu_workqueue
*workqueue
)
451 uatomic_or(&workqueue
->flags
, URCU_WORKQUEUE_PAUSE
);
452 cmm_smp_mb__after_uatomic_or();
453 wake_worker_thread(workqueue
);
455 while ((uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSED
) == 0)
456 (void) poll(NULL
, 0, 1);
459 /* To be used in after fork parent handler. */
460 void urcu_workqueue_resume_worker(struct urcu_workqueue
*workqueue
)
462 uatomic_and(&workqueue
->flags
, ~URCU_WORKQUEUE_PAUSE
);
463 while ((uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSED
) != 0)
464 (void) poll(NULL
, 0, 1);
467 void urcu_workqueue_create_worker(struct urcu_workqueue
*workqueue
)
471 /* Clear workqueue state from parent. */
472 workqueue
->flags
&= ~URCU_WORKQUEUE_PAUSED
;
473 workqueue
->flags
&= ~URCU_WORKQUEUE_PAUSE
;
475 ret
= pthread_create(&workqueue
->tid
, NULL
, workqueue_thread
, workqueue
);