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/cvs/libev/ev_iouring.c
Revision: 1.6
Committed: Fri Dec 20 05:20:23 2019 UTC (4 years, 6 months ago) by root
Content type: text/plain
Branch: MAIN
CVS Tags: rel-4_31, EV-rel-4_31
Changes since 1.5: +7 -7 lines
Log Message:
*** empty log message ***

File Contents

# Content
1 /*
2 * libev linux io_uring fd activity backend
3 *
4 * Copyright (c) 2019 Marc Alexander Lehmann <libev@schmorp.de>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without modifica-
8 * tion, are permitted provided that the following conditions are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright notice,
11 * this list of conditions and the following disclaimer.
12 *
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
19 * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
20 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
21 * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
23 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
24 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
25 * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
26 * OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Alternatively, the contents of this file may be used under the terms of
29 * the GNU General Public License ("GPL") version 2 or any later version,
30 * in which case the provisions of the GPL are applicable instead of
31 * the above. If you wish to allow the use of your version of this file
32 * only under the terms of the GPL and not to allow others to use your
33 * version of this file under the BSD license, indicate your decision
34 * by deleting the provisions above and replace them with the notice
35 * and other provisions required by the GPL. If you do not delete the
36 * provisions above, a recipient may use your version of this file under
37 * either the BSD or the GPL.
38 */
39
40 /*
41 * general notes about linux io_uring:
42 *
43 * a) it's the best interface I have seen so far. on linux.
44 * b) best is not necessarily very good.
45 * c) it's better than the aio mess, doesn't suffer from the fork problems
46 * of linux aio or epoll and so on and so on. and you could do event stuff
47 * without any syscalls. what's not to like?
48 * d) ok, it's vastly more complex, but that's ok, really.
49 * e) why 3 mmaps instead of one? one would be more space-efficient,
50 * and I can't see what benefit three would have (other than being
51 * somehow resizable/relocatable, but that's apparently not possible).
52 * f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and
53 the bizarre way structure offsets are commuinicated makes it hard to
54 * just print the ring buffer heads, even *iff* the memory were visible
55 * in gdb. but then, that's also ok, really.
56 * g) well, you cannot specify a timeout when waiting for events. no,
57 * seriously, the interface doesn't support a timeout. never seen _that_
58 * before. sure, you can use a timerfd, but that's another syscall
59 * you could have avoided. overall, this bizarre omission smells
60 * like a ยต-optimisation by the io_uring author for his personal
61 * applications, to the detriment of everybody else who just wants
62 * an event loop. but, umm, ok, if that's all, it could be worse.
63 * h) there is a hardcoded limit of 4096 outstanding events. okay,
64 * at least there is no arbitrary low system-wide limit...
65 * i) unlike linux aio, you *can* register more then the limit
66 * of fd events, and the kernel will "gracefully" signal an
67 * overflow, after which you could destroy and recreate the kernel
68 * state, a bit bigger, or fall back to e.g. poll. thats not
69 * totally insane, but kind of questions the point a high
70 * performance I/O framework when it doesn't really work
71 * under stress.
72 * j) but, oh my! is has exactly the same bugs as the linux aio backend,
73 * where some undocumented poll combinations just fail.
74 * so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course,
75 * this is completely undocumented, have I mantioned this already?
76 * k) overall, the *API* itself is, I dare to say, not a total trainwreck.
77 * the big isuess with it are the bugs requiring epoll, which might
78 * or might not get fixed (do I hold my breath?).
79 */
80
81 #include <sys/timerfd.h>
82 #include <sys/mman.h>
83 #include <poll.h>
84
85 #define IOURING_INIT_ENTRIES 32
86
87 /*****************************************************************************/
88 /* syscall wrapdadoop - this section has the raw api/abi definitions */
89
90 #include <linux/fs.h>
91 #include <linux/types.h>
92
93 /* mostly directly taken from the kernel or documentation */
94
95 struct io_uring_sqe
96 {
97 __u8 opcode;
98 __u8 flags;
99 __u16 ioprio;
100 __s32 fd;
101 __u64 off;
102 __u64 addr;
103 __u32 len;
104 union {
105 __kernel_rwf_t rw_flags;
106 __u32 fsync_flags;
107 __u16 poll_events;
108 __u32 sync_range_flags;
109 __u32 msg_flags;
110 };
111 __u64 user_data;
112 union {
113 __u16 buf_index;
114 __u64 __pad2[3];
115 };
116 };
117
118 struct io_uring_cqe
119 {
120 __u64 user_data;
121 __s32 res;
122 __u32 flags;
123 };
124
125 struct io_sqring_offsets
126 {
127 __u32 head;
128 __u32 tail;
129 __u32 ring_mask;
130 __u32 ring_entries;
131 __u32 flags;
132 __u32 dropped;
133 __u32 array;
134 __u32 resv1;
135 __u64 resv2;
136 };
137
138 struct io_cqring_offsets
139 {
140 __u32 head;
141 __u32 tail;
142 __u32 ring_mask;
143 __u32 ring_entries;
144 __u32 overflow;
145 __u32 cqes;
146 __u64 resv[2];
147 };
148
149 struct io_uring_params
150 {
151 __u32 sq_entries;
152 __u32 cq_entries;
153 __u32 flags;
154 __u32 sq_thread_cpu;
155 __u32 sq_thread_idle;
156 __u32 resv[5];
157 struct io_sqring_offsets sq_off;
158 struct io_cqring_offsets cq_off;
159 };
160
161 #define IORING_OP_POLL_ADD 6
162 #define IORING_OP_POLL_REMOVE 7
163
164 #define IORING_ENTER_GETEVENTS 0x01
165
166 #define IORING_OFF_SQ_RING 0x00000000ULL
167 #define IORING_OFF_CQ_RING 0x08000000ULL
168 #define IORING_OFF_SQES 0x10000000ULL
169
170 inline_size
171 int
172 evsys_io_uring_setup (unsigned entries, struct io_uring_params *params)
173 {
174 return ev_syscall2 (SYS_io_uring_setup, entries, params);
175 }
176
177 inline_size
178 int
179 evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz)
180 {
181 return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz);
182 }
183
184 /*****************************************************************************/
185 /* actual backed implementation */
186
187 /* we hope that volatile will make the compiler access this variables only once */
188 #define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name)
189 #define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name)
190
191 /* the index array */
192 #define EV_SQ_ARRAY ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array))
193
194 /* the submit/completion queue entries */
195 #define EV_SQES ((struct io_uring_sqe *) iouring_sqes)
196 #define EV_CQES ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes))
197
198 static
199 struct io_uring_sqe *
200 iouring_sqe_get (EV_P)
201 {
202 unsigned tail = EV_SQ_VAR (tail);
203
204 if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries))
205 {
206 /* queue full, flush */
207 evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0);
208 iouring_to_submit = 0;
209 }
210
211 assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)));
212
213 return EV_SQES + (tail & EV_SQ_VAR (ring_mask));
214 }
215
216 inline_size
217 struct io_uring_sqe *
218 iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe)
219 {
220 unsigned idx = sqe - EV_SQES;
221
222 EV_SQ_ARRAY [idx] = idx;
223 ECB_MEMORY_FENCE_RELEASE;
224 ++EV_SQ_VAR (tail);
225 /*ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */
226 ++iouring_to_submit;
227 }
228
229 /*****************************************************************************/
230
231 /* when the timerfd expires we simply note the fact,
232 * as the purpose of the timerfd is to wake us up, nothing else.
233 * the next iteration should re-set it.
234 */
235 static void
236 iouring_tfd_cb (EV_P_ struct ev_io *w, int revents)
237 {
238 iouring_tfd_to = EV_TSTAMP_HUGE;
239 }
240
241 static void
242 iouring_epoll_cb (EV_P_ struct ev_io *w, int revents)
243 {
244 epoll_poll (EV_A_ 0);
245 }
246
247 /* called for full and partial cleanup */
248 ecb_cold
249 static int
250 iouring_internal_destroy (EV_P)
251 {
252 close (iouring_tfd);
253 close (iouring_fd);
254
255 if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size);
256 if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size);
257 if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size );
258
259 if (ev_is_active (&iouring_epoll_w)) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_epoll_w);
260 if (ev_is_active (&iouring_tfd_w )) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_tfd_w );
261 }
262
263 ecb_cold
264 static int
265 iouring_internal_init (EV_P)
266 {
267 struct io_uring_params params = { 0 };
268
269 iouring_to_submit = 0;
270
271 iouring_tfd = -1;
272 iouring_sq_ring = MAP_FAILED;
273 iouring_cq_ring = MAP_FAILED;
274 iouring_sqes = MAP_FAILED;
275
276 for (;;)
277 {
278 iouring_fd = evsys_io_uring_setup (iouring_entries, &params);
279
280 if (iouring_fd >= 0)
281 break; /* yippie */
282
283 if (errno != EINVAL)
284 return -1; /* we failed */
285
286 /* EINVAL: lots of possible reasons, but maybe
287 * it is because we hit the unqueryable hardcoded size limit
288 */
289
290 /* we hit the limit already, give up */
291 if (iouring_max_entries)
292 return -1;
293
294 /* first time we hit EINVAL? assume we hit the limit, so go back and retry */
295 iouring_entries >>= 1;
296 iouring_max_entries = iouring_entries;
297 }
298
299 iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned);
300 iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe);
301 iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe);
302
303 iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE,
304 MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING);
305 iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE,
306 MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING);
307 iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE,
308 MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES);
309
310 if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED)
311 return -1;
312
313 iouring_sq_head = params.sq_off.head;
314 iouring_sq_tail = params.sq_off.tail;
315 iouring_sq_ring_mask = params.sq_off.ring_mask;
316 iouring_sq_ring_entries = params.sq_off.ring_entries;
317 iouring_sq_flags = params.sq_off.flags;
318 iouring_sq_dropped = params.sq_off.dropped;
319 iouring_sq_array = params.sq_off.array;
320
321 iouring_cq_head = params.cq_off.head;
322 iouring_cq_tail = params.cq_off.tail;
323 iouring_cq_ring_mask = params.cq_off.ring_mask;
324 iouring_cq_ring_entries = params.cq_off.ring_entries;
325 iouring_cq_overflow = params.cq_off.overflow;
326 iouring_cq_cqes = params.cq_off.cqes;
327
328 iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC);
329
330 if (iouring_tfd < 0)
331 return iouring_tfd;
332
333 iouring_tfd_to = EV_TSTAMP_HUGE;
334
335 return 0;
336 }
337
338 ecb_cold
339 static void
340 iouring_fork (EV_P)
341 {
342 iouring_internal_destroy (EV_A);
343
344 while (iouring_internal_init (EV_A) < 0)
345 ev_syserr ("(libev) io_uring_setup");
346
347 /* forking epoll should also effectively unregister all fds from the backend */
348 epoll_fork (EV_A);
349 /* epoll_fork already did this. hopefully */
350 /*fd_rearm_all (EV_A);*/
351
352 ev_io_stop (EV_A_ &iouring_epoll_w);
353 ev_io_set (EV_A_ &iouring_epoll_w, backend_fd, EV_READ);
354 ev_io_start (EV_A_ &iouring_epoll_w);
355
356 ev_io_stop (EV_A_ &iouring_tfd_w);
357 ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ);
358 ev_io_start (EV_A_ &iouring_tfd_w);
359 }
360
361 /*****************************************************************************/
362
363 static void
364 iouring_modify (EV_P_ int fd, int oev, int nev)
365 {
366 if (ecb_expect_false (anfds [fd].eflags))
367 {
368 /* we handed this fd over to epoll, so undo this first */
369 /* we do it manually because the optimisations on epoll_modify won't do us any good */
370 epoll_ctl (iouring_fd, EPOLL_CTL_DEL, fd, 0);
371 anfds [fd].eflags = 0;
372 oev = 0;
373 }
374
375 if (oev)
376 {
377 /* we assume the sqe's are all "properly" initialised */
378 struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
379 sqe->opcode = IORING_OP_POLL_REMOVE;
380 sqe->fd = fd;
381 sqe->user_data = -1;
382 iouring_sqe_submit (EV_A_ sqe);
383
384 /* increment generation counter to avoid handling old events */
385 ++anfds [fd].egen;
386 }
387
388 if (nev)
389 {
390 struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
391 sqe->opcode = IORING_OP_POLL_ADD;
392 sqe->fd = fd;
393 sqe->user_data = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32);
394 sqe->poll_events =
395 (nev & EV_READ ? POLLIN : 0)
396 | (nev & EV_WRITE ? POLLOUT : 0);
397 iouring_sqe_submit (EV_A_ sqe);
398 }
399 }
400
401 inline_size
402 void
403 iouring_tfd_update (EV_P_ ev_tstamp timeout)
404 {
405 ev_tstamp tfd_to = mn_now + timeout;
406
407 /* we assume there will be many iterations per timer change, so
408 * we only re-set the timerfd when we have to because its expiry
409 * is too late.
410 */
411 if (ecb_expect_false (tfd_to < iouring_tfd_to))
412 {
413 struct itimerspec its;
414
415 iouring_tfd_to = tfd_to;
416 EV_TS_SET (its.it_interval, 0.);
417 EV_TS_SET (its.it_value, tfd_to);
418
419 if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0)
420 assert (("libev: iouring timerfd_settime failed", 0));
421 }
422 }
423
424 inline_size
425 void
426 iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe)
427 {
428 int fd = cqe->user_data & 0xffffffffU;
429 uint32_t gen = cqe->user_data >> 32;
430 int res = cqe->res;
431
432 /* ignore fd removal events, if there are any. TODO: verify */
433 if (cqe->user_data == (__u64)-1)
434 abort ();//D
435
436 assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax));
437
438 /* documentation lies, of course. the result value is NOT like
439 * normal syscalls, but like linux raw syscalls, i.e. negative
440 * error numbers. fortunate, as otherwise there would be no way
441 * to get error codes at all. still, why not document this?
442 */
443
444 /* ignore event if generation doesn't match */
445 /* this should actually be very rare */
446 if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen))
447 return;
448
449 if (ecb_expect_false (res < 0))
450 {
451 if (res == -EINVAL)
452 {
453 /* we assume this error code means the fd/poll combination is buggy
454 * and fall back to epoll.
455 * this error code might also indicate a bug, but the kernel doesn't
456 * distinguish between those two conditions, so... sigh...
457 */
458
459 epoll_modify (EV_A_ fd, 0, anfds [fd].events);
460 }
461 else if (res == -EBADF)
462 {
463 assert (("libev: event loop rejected bad fd", res != -EBADF));
464 fd_kill (EV_A_ fd);
465 }
466 else
467 {
468 errno = -res;
469 ev_syserr ("(libev) IORING_OP_POLL_ADD");
470 }
471
472 return;
473 }
474
475 /* feed events, we do not expect or handle POLLNVAL */
476 fd_event (
477 EV_A_
478 fd,
479 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
480 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
481 );
482
483 /* io_uring is oneshot, so we need to re-arm the fd next iteration */
484 /* this also means we usually have to do at least one syscall per iteration */
485 anfds [fd].events = 0;
486 fd_change (EV_A_ fd, EV_ANFD_REIFY);
487 }
488
489 /* called when the event queue overflows */
490 ecb_cold
491 static void
492 iouring_overflow (EV_P)
493 {
494 /* we have two options, resize the queue (by tearing down
495 * everything and recreating it, or living with it
496 * and polling.
497 * we implement this by resizing tghe queue, and, if that fails,
498 * we just recreate the state on every failure, which
499 * kind of is a very inefficient poll.
500 * one danger is, due to the bios toward lower fds,
501 * we will only really get events for those, so
502 * maybe we need a poll() fallback, after all.
503 */
504 /*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */
505
506 fd_rearm_all (EV_A);
507
508 /* we double the size until we hit the hard-to-probe maximum */
509 if (!iouring_max_entries)
510 {
511 iouring_entries <<= 1;
512 iouring_fork (EV_A);
513 }
514 else
515 {
516 /* we hit the kernel limit, we should fall back to something else.
517 * we can either poll() a few times and hope for the best,
518 * poll always, or switch to epoll.
519 * since we use epoll anyways, go epoll.
520 */
521
522 iouring_internal_destroy (EV_A);
523
524 /* this should make it so that on return, we don'T call any uring functions */
525 iouring_to_submit = 0;
526
527 for (;;)
528 {
529 backend = epoll_init (EV_A_ 0);
530
531 if (backend)
532 break;
533
534 ev_syserr ("(libev) iouring switch to epoll");
535 }
536 }
537 }
538
539 /* handle any events in the completion queue, return true if there were any */
540 static int
541 iouring_handle_cq (EV_P)
542 {
543 unsigned head, tail, mask;
544
545 head = EV_CQ_VAR (head);
546 ECB_MEMORY_FENCE_ACQUIRE;
547 tail = EV_CQ_VAR (tail);
548
549 if (head == tail)
550 return 0;
551
552 /* it can only overflow if we have events, yes, yes? */
553 if (ecb_expect_false (EV_CQ_VAR (overflow)))
554 {
555 iouring_overflow (EV_A);
556 return 1;
557 }
558
559 mask = EV_CQ_VAR (ring_mask);
560
561 do
562 iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]);
563 while (head != tail);
564
565 EV_CQ_VAR (head) = head;
566 ECB_MEMORY_FENCE_RELEASE;
567
568 return 1;
569 }
570
571 static void
572 iouring_poll (EV_P_ ev_tstamp timeout)
573 {
574 /* if we have events, no need for extra syscalls, but we might have to queue events */
575 if (iouring_handle_cq (EV_A))
576 timeout = EV_TS_CONST (0.);
577 else
578 /* no events, so maybe wait for some */
579 iouring_tfd_update (EV_A_ timeout);
580
581 /* only enter the kernel if we have something to submit, or we need to wait */
582 if (timeout || iouring_to_submit)
583 {
584 int res;
585
586 EV_RELEASE_CB;
587
588 res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1,
589 timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0);
590 iouring_to_submit = 0;
591
592 EV_ACQUIRE_CB;
593
594 if (ecb_expect_false (res < 0))
595 if (errno == EINTR)
596 /* ignore */;
597 else
598 ev_syserr ("(libev) iouring setup");
599 else
600 iouring_handle_cq (EV_A);
601 }
602 }
603
604 inline_size
605 int
606 iouring_init (EV_P_ int flags)
607 {
608 if (!epoll_init (EV_A_ 0))
609 return 0;
610
611 iouring_entries = IOURING_INIT_ENTRIES;
612 iouring_max_entries = 0;
613
614 if (iouring_internal_init (EV_A) < 0)
615 {
616 iouring_internal_destroy (EV_A);
617 return 0;
618 }
619
620 ev_io_init (&iouring_epoll_w, iouring_epoll_cb, backend_fd, EV_READ);
621 ev_set_priority (&iouring_epoll_w, EV_MAXPRI);
622
623 ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ);
624 ev_set_priority (&iouring_tfd_w, EV_MAXPRI);
625
626 ev_io_start (EV_A_ &iouring_epoll_w);
627 ev_unref (EV_A); /* watcher should not keep loop alive */
628
629 ev_io_start (EV_A_ &iouring_tfd_w);
630 ev_unref (EV_A); /* watcher should not keep loop alive */
631
632 backend_modify = iouring_modify;
633 backend_poll = iouring_poll;
634
635 return EVBACKEND_IOURING;
636 }
637
638 inline_size
639 void
640 iouring_destroy (EV_P)
641 {
642 iouring_internal_destroy (EV_A);
643 epoll_destroy (EV_A);
644 }
645