4 * Userspace RCU library - batch memory reclamation with kernel API
6 * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
39 #include "urcu/wfqueue.h"
40 #include "urcu-call-rcu.h"
41 #include "urcu-pointer.h"
42 #include "urcu/list.h"
43 #include "urcu/futex.h"
45 /* Data structure that identifies a call_rcu thread. */
47 struct call_rcu_data
{
48 struct cds_wfq_queue cbs
;
51 unsigned long qlen
; /* maintained for debugging. */
54 struct cds_list_head list
;
55 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
58 * List of all call_rcu_data structures to keep valgrind happy.
59 * Protected by call_rcu_mutex.
62 CDS_LIST_HEAD(call_rcu_data_list
);
64 /* Link a thread using call_rcu() to its call_rcu thread. */
66 static __thread
struct call_rcu_data
*thread_call_rcu_data
;
68 /* Guard call_rcu thread creation. */
70 static pthread_mutex_t call_rcu_mutex
= PTHREAD_MUTEX_INITIALIZER
;
72 /* If a given thread does not have its own call_rcu thread, this is default. */
74 static struct call_rcu_data
*default_call_rcu_data
;
77 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
78 * available, then we can have call_rcu threads assigned to individual
79 * CPUs rather than only to specific threads.
82 #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
85 * Pointer to array of pointers to per-CPU call_rcu_data structures
89 static struct call_rcu_data
**per_cpu_call_rcu_data
;
92 static void call_rcu_wait(struct call_rcu_data
*crdp
)
94 /* Read call_rcu list before read futex */
96 if (uatomic_read(&crdp
->futex
) == -1)
97 futex_async(&crdp
->futex
, FUTEX_WAIT
, -1,
101 static void call_rcu_wake_up(struct call_rcu_data
*crdp
)
103 /* Write to call_rcu list before reading/writing futex */
105 if (unlikely(uatomic_read(&crdp
->futex
) == -1)) {
106 uatomic_set(&crdp
->futex
, 0);
107 futex_async(&crdp
->futex
, FUTEX_WAKE
, 1,
112 /* Allocate the array if it has not already been allocated. */
114 static void alloc_cpu_call_rcu_data(void)
116 struct call_rcu_data
**p
;
117 static int warned
= 0;
121 maxcpus
= sysconf(_SC_NPROCESSORS_CONF
);
125 p
= malloc(maxcpus
* sizeof(*per_cpu_call_rcu_data
));
127 memset(p
, '\0', maxcpus
* sizeof(*per_cpu_call_rcu_data
));
128 per_cpu_call_rcu_data
= p
;
131 fprintf(stderr
, "[error] liburcu: unable to allocate per-CPU pointer array\n");
137 #else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
139 static const struct call_rcu_data
**per_cpu_call_rcu_data
= NULL
;
140 static const long maxcpus
= -1;
142 static void alloc_cpu_call_rcu_data(void)
146 static int sched_getcpu(void)
151 #endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
153 /* Acquire the specified pthread mutex. */
155 static void call_rcu_lock(pthread_mutex_t
*pmp
)
157 if (pthread_mutex_lock(pmp
) != 0) {
158 perror("pthread_mutex_lock");
163 /* Release the specified pthread mutex. */
165 static void call_rcu_unlock(pthread_mutex_t
*pmp
)
167 if (pthread_mutex_unlock(pmp
) != 0) {
168 perror("pthread_mutex_unlock");
173 #if HAVE_SCHED_SETAFFINITY
175 int set_thread_cpu_affinity(struct call_rcu_data
*crdp
)
179 if (crdp
->cpu_affinity
< 0)
183 CPU_SET(crdp
->cpu_affinity
, &mask
);
184 #if SCHED_SETAFFINITY_ARGS == 2
185 return sched_setaffinity(0, &mask
);
187 return sched_setaffinity(0, sizeof(mask
), &mask
);
192 int set_thread_cpu_affinity(struct call_rcu_data
*crdp
)
198 /* This is the code run by each call_rcu thread. */
200 static void *call_rcu_thread(void *arg
)
202 unsigned long cbcount
;
203 struct cds_wfq_node
*cbs
;
204 struct cds_wfq_node
**cbs_tail
;
205 struct call_rcu_data
*crdp
= (struct call_rcu_data
*)arg
;
206 struct rcu_head
*rhp
;
207 int rt
= !!(uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_RT
);
209 if (set_thread_cpu_affinity(crdp
) != 0) {
210 perror("pthread_setaffinity_np");
214 thread_call_rcu_data
= crdp
;
216 uatomic_dec(&crdp
->futex
);
217 /* Decrement futex before reading call_rcu list */
221 if (&crdp
->cbs
.head
!= _CMM_LOAD_SHARED(crdp
->cbs
.tail
)) {
222 while ((cbs
= _CMM_LOAD_SHARED(crdp
->cbs
.head
)) == NULL
)
224 _CMM_STORE_SHARED(crdp
->cbs
.head
, NULL
);
225 cbs_tail
= (struct cds_wfq_node
**)
226 uatomic_xchg(&crdp
->cbs
.tail
, &crdp
->cbs
.head
);
230 while (cbs
->next
== NULL
&&
231 &cbs
->next
!= cbs_tail
)
233 if (cbs
== &crdp
->cbs
.dummy
) {
237 rhp
= (struct rcu_head
*)cbs
;
241 } while (cbs
!= NULL
);
242 uatomic_sub(&crdp
->qlen
, cbcount
);
244 if (uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOP
)
248 == _CMM_LOAD_SHARED(crdp
->cbs
.tail
)) {
251 uatomic_dec(&crdp
->futex
);
253 * Decrement futex before reading
266 * Read call_rcu list before write futex.
269 uatomic_set(&crdp
->futex
, 0);
271 uatomic_or(&crdp
->flags
, URCU_CALL_RCU_STOPPED
);
276 * Create both a call_rcu thread and the corresponding call_rcu_data
277 * structure, linking the structure in as specified. Caller must hold
281 static void call_rcu_data_init(struct call_rcu_data
**crdpp
,
285 struct call_rcu_data
*crdp
;
287 crdp
= malloc(sizeof(*crdp
));
289 fprintf(stderr
, "Out of memory.\n");
292 memset(crdp
, '\0', sizeof(*crdp
));
293 cds_wfq_init(&crdp
->cbs
);
297 cds_list_add(&crdp
->list
, &call_rcu_data_list
);
298 crdp
->cpu_affinity
= cpu_affinity
;
299 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
301 if (pthread_create(&crdp
->tid
, NULL
, call_rcu_thread
, crdp
) != 0) {
302 perror("pthread_create");
308 * Return a pointer to the call_rcu_data structure for the specified
309 * CPU, returning NULL if there is none. We cannot automatically
310 * created it because the platform we are running on might not define
314 struct call_rcu_data
*get_cpu_call_rcu_data(int cpu
)
316 static int warned
= 0;
318 if (per_cpu_call_rcu_data
== NULL
)
320 if (!warned
&& maxcpus
> 0 && (cpu
< 0 || maxcpus
<= cpu
)) {
321 fprintf(stderr
, "[error] liburcu: get CPU # out of range\n");
324 if (cpu
< 0 || maxcpus
<= cpu
)
326 return per_cpu_call_rcu_data
[cpu
];
330 * Return the tid corresponding to the call_rcu thread whose
331 * call_rcu_data structure is specified.
334 pthread_t
get_call_rcu_thread(struct call_rcu_data
*crdp
)
340 * Create a call_rcu_data structure (with thread) and return a pointer.
343 static struct call_rcu_data
*__create_call_rcu_data(unsigned long flags
,
346 struct call_rcu_data
*crdp
;
348 call_rcu_data_init(&crdp
, flags
, cpu_affinity
);
352 struct call_rcu_data
*create_call_rcu_data(unsigned long flags
,
355 struct call_rcu_data
*crdp
;
357 call_rcu_lock(&call_rcu_mutex
);
358 crdp
= __create_call_rcu_data(flags
, cpu_affinity
);
359 call_rcu_unlock(&call_rcu_mutex
);
364 * Set the specified CPU to use the specified call_rcu_data structure.
366 * Use NULL to remove a CPU's call_rcu_data structure, but it is
367 * the caller's responsibility to dispose of the removed structure.
368 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
369 * (prior to NULLing it out, of course).
372 int set_cpu_call_rcu_data(int cpu
, struct call_rcu_data
*crdp
)
376 call_rcu_lock(&call_rcu_mutex
);
377 if (cpu
< 0 || maxcpus
<= cpu
) {
379 fprintf(stderr
, "[error] liburcu: set CPU # out of range\n");
382 call_rcu_unlock(&call_rcu_mutex
);
386 alloc_cpu_call_rcu_data();
387 call_rcu_unlock(&call_rcu_mutex
);
388 if (per_cpu_call_rcu_data
== NULL
) {
392 per_cpu_call_rcu_data
[cpu
] = crdp
;
397 * Return a pointer to the default call_rcu_data structure, creating
398 * one if need be. Because we never free call_rcu_data structures,
399 * we don't need to be in an RCU read-side critical section.
402 struct call_rcu_data
*get_default_call_rcu_data(void)
404 if (default_call_rcu_data
!= NULL
)
405 return rcu_dereference(default_call_rcu_data
);
406 call_rcu_lock(&call_rcu_mutex
);
407 if (default_call_rcu_data
!= NULL
) {
408 call_rcu_unlock(&call_rcu_mutex
);
409 return default_call_rcu_data
;
411 call_rcu_data_init(&default_call_rcu_data
, 0, -1);
412 call_rcu_unlock(&call_rcu_mutex
);
413 return default_call_rcu_data
;
417 * Return the call_rcu_data structure that applies to the currently
418 * running thread. Any call_rcu_data structure assigned specifically
419 * to this thread has first priority, followed by any call_rcu_data
420 * structure assigned to the CPU on which the thread is running,
421 * followed by the default call_rcu_data structure. If there is not
422 * yet a default call_rcu_data structure, one will be created.
424 struct call_rcu_data
*get_call_rcu_data(void)
427 static int warned
= 0;
429 if (thread_call_rcu_data
!= NULL
)
430 return thread_call_rcu_data
;
432 return get_default_call_rcu_data();
433 curcpu
= sched_getcpu();
434 if (!warned
&& (curcpu
< 0 || maxcpus
<= curcpu
)) {
435 fprintf(stderr
, "[error] liburcu: gcrd CPU # out of range\n");
438 if (curcpu
>= 0 && maxcpus
> curcpu
&&
439 per_cpu_call_rcu_data
!= NULL
&&
440 per_cpu_call_rcu_data
[curcpu
] != NULL
)
441 return per_cpu_call_rcu_data
[curcpu
];
442 return get_default_call_rcu_data();
446 * Return a pointer to this task's call_rcu_data if there is one.
449 struct call_rcu_data
*get_thread_call_rcu_data(void)
451 return thread_call_rcu_data
;
455 * Set this task's call_rcu_data structure as specified, regardless
456 * of whether or not this task already had one. (This allows switching
457 * to and from real-time call_rcu threads, for example.)
459 * Use NULL to remove a thread's call_rcu_data structure, but it is
460 * the caller's responsibility to dispose of the removed structure.
461 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
462 * (prior to NULLing it out, of course).
465 void set_thread_call_rcu_data(struct call_rcu_data
*crdp
)
467 thread_call_rcu_data
= crdp
;
471 * Create a separate call_rcu thread for each CPU. This does not
472 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
473 * function if you want that behavior.
476 int create_all_cpu_call_rcu_data(unsigned long flags
)
479 struct call_rcu_data
*crdp
;
482 call_rcu_lock(&call_rcu_mutex
);
483 alloc_cpu_call_rcu_data();
484 call_rcu_unlock(&call_rcu_mutex
);
489 if (per_cpu_call_rcu_data
== NULL
) {
493 for (i
= 0; i
< maxcpus
; i
++) {
494 call_rcu_lock(&call_rcu_mutex
);
495 if (get_cpu_call_rcu_data(i
)) {
496 call_rcu_unlock(&call_rcu_mutex
);
499 crdp
= __create_call_rcu_data(flags
, i
);
501 call_rcu_unlock(&call_rcu_mutex
);
505 call_rcu_unlock(&call_rcu_mutex
);
506 if ((ret
= set_cpu_call_rcu_data(i
, crdp
)) != 0) {
507 /* FIXME: Leaks crdp for now. */
508 return ret
; /* Can happen on race. */
515 * Wake up the call_rcu thread corresponding to the specified
516 * call_rcu_data structure.
518 static void wake_call_rcu_thread(struct call_rcu_data
*crdp
)
520 if (!(_CMM_LOAD_SHARED(crdp
->flags
) & URCU_CALL_RCU_RT
))
521 call_rcu_wake_up(crdp
);
525 * Schedule a function to be invoked after a following grace period.
526 * This is the only function that must be called -- the others are
527 * only present to allow applications to tune their use of RCU for
528 * maximum performance.
530 * Note that unless a call_rcu thread has not already been created,
531 * the first invocation of call_rcu() will create one. So, if you
532 * need the first invocation of call_rcu() to be fast, make sure
533 * to create a call_rcu thread first. One way to accomplish this is
534 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
537 void call_rcu(struct rcu_head
*head
,
538 void (*func
)(struct rcu_head
*head
))
540 struct call_rcu_data
*crdp
;
542 cds_wfq_node_init(&head
->next
);
544 crdp
= get_call_rcu_data();
545 cds_wfq_enqueue(&crdp
->cbs
, &head
->next
);
546 uatomic_inc(&crdp
->qlen
);
547 wake_call_rcu_thread(crdp
);
551 * Free up the specified call_rcu_data structure, terminating the
552 * associated call_rcu thread. The caller must have previously
553 * removed the call_rcu_data structure from per-thread or per-CPU
554 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
555 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
556 * per-thread call_rcu_data structures.
558 * We silently refuse to free up the default call_rcu_data structure
559 * because that is where we put any leftover callbacks. Note that
560 * the possibility of self-spawning callbacks makes it impossible
561 * to execute all the callbacks in finite time without putting any
562 * newly spawned callbacks somewhere else. The "somewhere else" of
563 * last resort is the default call_rcu_data structure.
565 * We also silently refuse to free NULL pointers. This simplifies
568 void call_rcu_data_free(struct call_rcu_data
*crdp
)
570 struct cds_wfq_node
*cbs
;
571 struct cds_wfq_node
**cbs_tail
;
572 struct cds_wfq_node
**cbs_endprev
;
574 if (crdp
== NULL
|| crdp
== default_call_rcu_data
) {
577 if ((uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOPPED
) == 0) {
578 uatomic_or(&crdp
->flags
, URCU_CALL_RCU_STOP
);
579 wake_call_rcu_thread(crdp
);
580 while ((uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOPPED
) == 0)
583 if (&crdp
->cbs
.head
!= _CMM_LOAD_SHARED(crdp
->cbs
.tail
)) {
584 while ((cbs
= _CMM_LOAD_SHARED(crdp
->cbs
.head
)) == NULL
)
586 _CMM_STORE_SHARED(crdp
->cbs
.head
, NULL
);
587 cbs_tail
= (struct cds_wfq_node
**)
588 uatomic_xchg(&crdp
->cbs
.tail
, &crdp
->cbs
.head
);
589 cbs_endprev
= (struct cds_wfq_node
**)
590 uatomic_xchg(&default_call_rcu_data
, cbs_tail
);
592 uatomic_add(&default_call_rcu_data
->qlen
,
593 uatomic_read(&crdp
->qlen
));
594 cds_list_del(&crdp
->list
);
600 * Clean up all the per-CPU call_rcu threads.
602 void free_all_cpu_call_rcu_data(void)
605 struct call_rcu_data
*crdp
;
609 for (cpu
= 0; cpu
< maxcpus
; cpu
++) {
610 crdp
= get_cpu_call_rcu_data(cpu
);
613 set_cpu_call_rcu_data(cpu
, NULL
);
614 call_rcu_data_free(crdp
);
619 * Acquire the call_rcu_mutex in order to ensure that the child sees
620 * all of the call_rcu() data structures in a consistent state.
621 * Suitable for pthread_atfork() and friends.
623 void call_rcu_before_fork(void)
625 call_rcu_lock(&call_rcu_mutex
);
629 * Clean up call_rcu data structures in the parent of a successful fork()
630 * that is not followed by exec() in the child. Suitable for
631 * pthread_atfork() and friends.
633 void call_rcu_after_fork_parent(void)
635 call_rcu_unlock(&call_rcu_mutex
);
639 * Clean up call_rcu data structures in the child of a successful fork()
640 * that is not followed by exec(). Suitable for pthread_atfork() and
643 void call_rcu_after_fork_child(void)
645 struct call_rcu_data
*crdp
;
647 /* Release the mutex. */
648 call_rcu_unlock(&call_rcu_mutex
);
651 * Allocate a new default call_rcu_data structure in order
652 * to get a working call_rcu thread to go with it.
654 default_call_rcu_data
= NULL
;
655 (void)get_default_call_rcu_data();
657 /* Dispose of all of the rest of the call_rcu_data structures. */
658 while (call_rcu_data_list
.next
!= call_rcu_data_list
.prev
) {
659 crdp
= cds_list_entry(call_rcu_data_list
.prev
,
660 struct call_rcu_data
, list
);
661 if (crdp
== default_call_rcu_data
)
662 crdp
= cds_list_entry(crdp
->list
.prev
,
663 struct call_rcu_data
, list
);
664 uatomic_set(&crdp
->flags
, URCU_CALL_RCU_STOPPED
);
665 call_rcu_data_free(crdp
);