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Revision: 1.9
Committed: Fri Dec 27 16:15:58 2019 UTC (4 years, 6 months ago) by root
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Branch: MAIN
Changes since 1.8: +4 -0 lines
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# 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 * (FIXME: newer kernels can use 2 mmaps only, need to look into this).
53 * f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and
54 * the bizarre way structure offsets are communicated makes it hard to
55 * just print the ring buffer heads, even *iff* the memory were visible
56 * in gdb. but then, that's also ok, really.
57 * g) well, you cannot specify a timeout when waiting for events. no,
58 * seriously, the interface doesn't support a timeout. never seen _that_
59 * before. sure, you can use a timerfd, but that's another syscall
60 * you could have avoided. overall, this bizarre omission smells
61 * like a ยต-optimisation by the io_uring author for his personal
62 * applications, to the detriment of everybody else who just wants
63 * an event loop. but, umm, ok, if that's all, it could be worse.
64 * (FIXME: jens mentioned timeout commands, need to investigate)
65 * h) there is a hardcoded limit of 4096 outstanding events. okay,
66 * at least there is no arbitrary low system-wide limit...
67 * (FIXME: apparently, this was increased to 32768 in later kernels(
68 * i) unlike linux aio, you *can* register more then the limit
69 * of fd events, and the kernel will "gracefully" signal an
70 * overflow, after which you could destroy and recreate the kernel
71 * state, a bit bigger, or fall back to e.g. poll. thats not
72 * totally insane, but kind of questions the point a high
73 * performance I/O framework when it doesn't really work
74 * under stress.
75 * (FIXME: iouring should no longer drop events, need to investigate)
76 * j) but, oh my! is has exactly the same bugs as the linux aio backend,
77 * where some undocumented poll combinations just fail.
78 * so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course,
79 * this is completely undocumented, have I mantioned this already?
80 * k) overall, the *API* itself is, I dare to say, not a total trainwreck.
81 * the big isuess with it are the bugs requiring epoll, which might
82 * or might not get fixed (do I hold my breath?).
83 */
84
85 /* TODO: use internal TIMEOUT */
86 /* TODO: take advantage of single mmap, NODROP etc. */
87 /* TODO: resize cq/sq size independently */
88
89 #include <sys/timerfd.h>
90 #include <sys/mman.h>
91 #include <poll.h>
92
93 #define IOURING_INIT_ENTRIES 32
94
95 /*****************************************************************************/
96 /* syscall wrapdadoop - this section has the raw api/abi definitions */
97
98 #include <linux/fs.h>
99 #include <linux/types.h>
100
101 /* mostly directly taken from the kernel or documentation */
102
103 struct io_uring_sqe
104 {
105 __u8 opcode;
106 __u8 flags;
107 __u16 ioprio;
108 __s32 fd;
109 union {
110 __u64 off;
111 __u64 addr2;
112 };
113 __u64 addr;
114 __u32 len;
115 union {
116 __kernel_rwf_t rw_flags;
117 __u32 fsync_flags;
118 __u16 poll_events;
119 __u32 sync_range_flags;
120 __u32 msg_flags;
121 __u32 timeout_flags;
122 __u32 accept_flags;
123 __u32 cancel_flags;
124 __u32 open_flags;
125 __u32 statx_flags;
126 };
127 __u64 user_data;
128 union {
129 __u16 buf_index;
130 __u64 __pad2[3];
131 };
132 };
133
134 struct io_uring_cqe
135 {
136 __u64 user_data;
137 __s32 res;
138 __u32 flags;
139 };
140
141 struct io_sqring_offsets
142 {
143 __u32 head;
144 __u32 tail;
145 __u32 ring_mask;
146 __u32 ring_entries;
147 __u32 flags;
148 __u32 dropped;
149 __u32 array;
150 __u32 resv1;
151 __u64 resv2;
152 };
153
154 struct io_cqring_offsets
155 {
156 __u32 head;
157 __u32 tail;
158 __u32 ring_mask;
159 __u32 ring_entries;
160 __u32 overflow;
161 __u32 cqes;
162 __u64 resv[2];
163 };
164
165 struct io_uring_params
166 {
167 __u32 sq_entries;
168 __u32 cq_entries;
169 __u32 flags;
170 __u32 sq_thread_cpu;
171 __u32 sq_thread_idle;
172 __u32 features;
173 __u32 resv[4];
174 struct io_sqring_offsets sq_off;
175 struct io_cqring_offsets cq_off;
176 };
177
178 #define IORING_OP_POLL_ADD 6
179 #define IORING_OP_POLL_REMOVE 7
180
181 #define IORING_ENTER_GETEVENTS 0x01
182
183 #define IORING_OFF_SQ_RING 0x00000000ULL
184 #define IORING_OFF_CQ_RING 0x08000000ULL
185 #define IORING_OFF_SQES 0x10000000ULL
186
187 #define IORING_FEAT_SINGLE_MMAP 0x1
188 #define IORING_FEAT_NODROP 0x2
189 #define IORING_FEAT_SUBMIT_STABLE 0x4
190
191 inline_size
192 int
193 evsys_io_uring_setup (unsigned entries, struct io_uring_params *params)
194 {
195 return ev_syscall2 (SYS_io_uring_setup, entries, params);
196 }
197
198 inline_size
199 int
200 evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz)
201 {
202 return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz);
203 }
204
205 /*****************************************************************************/
206 /* actual backed implementation */
207
208 /* we hope that volatile will make the compiler access this variables only once */
209 #define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name)
210 #define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name)
211
212 /* the index array */
213 #define EV_SQ_ARRAY ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array))
214
215 /* the submit/completion queue entries */
216 #define EV_SQES ((struct io_uring_sqe *) iouring_sqes)
217 #define EV_CQES ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes))
218
219 static
220 struct io_uring_sqe *
221 iouring_sqe_get (EV_P)
222 {
223 unsigned tail = EV_SQ_VAR (tail);
224
225 if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries))
226 {
227 /* queue full, flush */
228 evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0);
229 iouring_to_submit = 0;
230 }
231
232 assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)));
233
234 return EV_SQES + (tail & EV_SQ_VAR (ring_mask));
235 }
236
237 inline_size
238 struct io_uring_sqe *
239 iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe)
240 {
241 unsigned idx = sqe - EV_SQES;
242
243 EV_SQ_ARRAY [idx] = idx;
244 ECB_MEMORY_FENCE_RELEASE;
245 ++EV_SQ_VAR (tail);
246 /*ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */
247 ++iouring_to_submit;
248 }
249
250 /*****************************************************************************/
251
252 /* when the timerfd expires we simply note the fact,
253 * as the purpose of the timerfd is to wake us up, nothing else.
254 * the next iteration should re-set it.
255 */
256 static void
257 iouring_tfd_cb (EV_P_ struct ev_io *w, int revents)
258 {
259 iouring_tfd_to = EV_TSTAMP_HUGE;
260 }
261
262 /* called for full and partial cleanup */
263 ecb_cold
264 static int
265 iouring_internal_destroy (EV_P)
266 {
267 close (iouring_tfd);
268 close (iouring_fd);
269
270 if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size);
271 if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size);
272 if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size );
273
274 if (ev_is_active (&iouring_tfd_w))
275 {
276 ev_ref (EV_A);
277 ev_io_stop (EV_A_ &iouring_tfd_w);
278 }
279 }
280
281 ecb_cold
282 static int
283 iouring_internal_init (EV_P)
284 {
285 struct io_uring_params params = { 0 };
286
287 iouring_to_submit = 0;
288
289 iouring_tfd = -1;
290 iouring_sq_ring = MAP_FAILED;
291 iouring_cq_ring = MAP_FAILED;
292 iouring_sqes = MAP_FAILED;
293
294 for (;;)
295 {
296 iouring_fd = evsys_io_uring_setup (iouring_entries, &params);
297
298 if (iouring_fd >= 0)
299 break; /* yippie */
300
301 if (errno != EINVAL)
302 return -1; /* we failed */
303
304 /* EINVAL: lots of possible reasons, but maybe
305 * it is because we hit the unqueryable hardcoded size limit
306 */
307
308 /* we hit the limit already, give up */
309 if (iouring_max_entries)
310 return -1;
311
312 /* first time we hit EINVAL? assume we hit the limit, so go back and retry */
313 iouring_entries >>= 1;
314 iouring_max_entries = iouring_entries;
315 }
316
317 iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned);
318 iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe);
319 iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe);
320
321 iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE,
322 MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING);
323 iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE,
324 MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING);
325 iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE,
326 MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES);
327
328 if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED)
329 return -1;
330
331 iouring_sq_head = params.sq_off.head;
332 iouring_sq_tail = params.sq_off.tail;
333 iouring_sq_ring_mask = params.sq_off.ring_mask;
334 iouring_sq_ring_entries = params.sq_off.ring_entries;
335 iouring_sq_flags = params.sq_off.flags;
336 iouring_sq_dropped = params.sq_off.dropped;
337 iouring_sq_array = params.sq_off.array;
338
339 iouring_cq_head = params.cq_off.head;
340 iouring_cq_tail = params.cq_off.tail;
341 iouring_cq_ring_mask = params.cq_off.ring_mask;
342 iouring_cq_ring_entries = params.cq_off.ring_entries;
343 iouring_cq_overflow = params.cq_off.overflow;
344 iouring_cq_cqes = params.cq_off.cqes;
345
346 iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC);
347
348 if (iouring_tfd < 0)
349 return iouring_tfd;
350
351 iouring_tfd_to = EV_TSTAMP_HUGE;
352
353 return 0;
354 }
355
356 ecb_cold
357 static void
358 iouring_fork (EV_P)
359 {
360 iouring_internal_destroy (EV_A);
361
362 while (iouring_internal_init (EV_A) < 0)
363 ev_syserr ("(libev) io_uring_setup");
364
365 fd_rearm_all (EV_A);
366
367 ev_io_stop (EV_A_ &iouring_tfd_w);
368 ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ);
369 ev_io_start (EV_A_ &iouring_tfd_w);
370 }
371
372 /*****************************************************************************/
373
374 static void
375 iouring_modify (EV_P_ int fd, int oev, int nev)
376 {
377 if (oev)
378 {
379 /* we assume the sqe's are all "properly" initialised */
380 struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
381 sqe->opcode = IORING_OP_POLL_REMOVE;
382 sqe->fd = fd;
383 sqe->user_data = -1;
384 iouring_sqe_submit (EV_A_ sqe);
385
386 /* increment generation counter to avoid handling old events */
387 ++anfds [fd].egen;
388 }
389
390 if (nev)
391 {
392 struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
393 sqe->opcode = IORING_OP_POLL_ADD;
394 sqe->fd = fd;
395 sqe->user_data = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32);
396 sqe->poll_events =
397 (nev & EV_READ ? POLLIN : 0)
398 | (nev & EV_WRITE ? POLLOUT : 0);
399 iouring_sqe_submit (EV_A_ sqe);
400 }
401 }
402
403 inline_size
404 void
405 iouring_tfd_update (EV_P_ ev_tstamp timeout)
406 {
407 ev_tstamp tfd_to = mn_now + timeout;
408
409 /* we assume there will be many iterations per timer change, so
410 * we only re-set the timerfd when we have to because its expiry
411 * is too late.
412 */
413 if (ecb_expect_false (tfd_to < iouring_tfd_to))
414 {
415 struct itimerspec its;
416
417 iouring_tfd_to = tfd_to;
418 EV_TS_SET (its.it_interval, 0.);
419 EV_TS_SET (its.it_value, tfd_to);
420
421 if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0)
422 assert (("libev: iouring timerfd_settime failed", 0));
423 }
424 }
425
426 inline_size
427 void
428 iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe)
429 {
430 int fd = cqe->user_data & 0xffffffffU;
431 uint32_t gen = cqe->user_data >> 32;
432 int res = cqe->res;
433
434 /* ignore fd removal events, if there are any. TODO: verify */
435 if (cqe->user_data == (__u64)-1)
436 abort ();//D
437
438 assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax));
439
440 /* documentation lies, of course. the result value is NOT like
441 * normal syscalls, but like linux raw syscalls, i.e. negative
442 * error numbers. fortunate, as otherwise there would be no way
443 * to get error codes at all. still, why not document this?
444 */
445
446 /* ignore event if generation doesn't match */
447 /* this should actually be very rare */
448 if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen))
449 return;
450
451 if (ecb_expect_false (res < 0))
452 {
453 //TODO: EINVAL handling (was something failed with this fd)
454 //TODO: EBUSY happens when?
455
456 if (res == -EBADF)
457 {
458 assert (("libev: event loop rejected bad fd", res != -EBADF));
459 fd_kill (EV_A_ fd);
460 }
461 else
462 {
463 errno = -res;
464 ev_syserr ("(libev) IORING_OP_POLL_ADD");
465 }
466
467 return;
468 }
469
470 /* feed events, we do not expect or handle POLLNVAL */
471 fd_event (
472 EV_A_
473 fd,
474 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
475 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
476 );
477
478 /* io_uring is oneshot, so we need to re-arm the fd next iteration */
479 /* this also means we usually have to do at least one syscall per iteration */
480 anfds [fd].events = 0;
481 fd_change (EV_A_ fd, EV_ANFD_REIFY);
482 }
483
484 /* called when the event queue overflows */
485 ecb_cold
486 static void
487 iouring_overflow (EV_P)
488 {
489 /* we have two options, resize the queue (by tearing down
490 * everything and recreating it, or living with it
491 * and polling.
492 * we implement this by resizing tghe queue, and, if that fails,
493 * we just recreate the state on every failure, which
494 * kind of is a very inefficient poll.
495 * one danger is, due to the bios toward lower fds,
496 * we will only really get events for those, so
497 * maybe we need a poll() fallback, after all.
498 */
499 /*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */
500
501 fd_rearm_all (EV_A);
502
503 /* we double the size until we hit the hard-to-probe maximum */
504 if (!iouring_max_entries)
505 {
506 iouring_entries <<= 1;
507 iouring_fork (EV_A);
508 }
509 else
510 {
511 /* we hit the kernel limit, we should fall back to something else.
512 * we can either poll() a few times and hope for the best,
513 * poll always, or switch to epoll.
514 * since we use epoll anyways, go epoll.
515 */
516
517 iouring_internal_destroy (EV_A);
518
519 /* this should make it so that on return, we don'T call any uring functions */
520 iouring_to_submit = 0;
521
522 for (;;)
523 {
524 backend = epoll_init (EV_A_ 0);
525
526 if (backend)
527 break;
528
529 ev_syserr ("(libev) iouring switch to epoll");
530 }
531 }
532 }
533
534 /* handle any events in the completion queue, return true if there were any */
535 static int
536 iouring_handle_cq (EV_P)
537 {
538 unsigned head, tail, mask;
539
540 head = EV_CQ_VAR (head);
541 ECB_MEMORY_FENCE_ACQUIRE;
542 tail = EV_CQ_VAR (tail);
543
544 if (head == tail)
545 return 0;
546
547 /* it can only overflow if we have events, yes, yes? */
548 if (ecb_expect_false (EV_CQ_VAR (overflow)))
549 {
550 iouring_overflow (EV_A);
551 return 1;
552 }
553
554 mask = EV_CQ_VAR (ring_mask);
555
556 do
557 iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]);
558 while (head != tail);
559
560 EV_CQ_VAR (head) = head;
561 ECB_MEMORY_FENCE_RELEASE;
562
563 return 1;
564 }
565
566 static void
567 iouring_poll (EV_P_ ev_tstamp timeout)
568 {
569 /* if we have events, no need for extra syscalls, but we might have to queue events */
570 if (iouring_handle_cq (EV_A))
571 timeout = EV_TS_CONST (0.);
572 else
573 /* no events, so maybe wait for some */
574 iouring_tfd_update (EV_A_ timeout);
575
576 /* only enter the kernel if we have something to submit, or we need to wait */
577 if (timeout || iouring_to_submit)
578 {
579 int res;
580
581 EV_RELEASE_CB;
582
583 res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1,
584 timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0);
585 iouring_to_submit = 0;
586
587 EV_ACQUIRE_CB;
588
589 if (ecb_expect_false (res < 0))
590 if (errno == EINTR)
591 /* ignore */;
592 else
593 ev_syserr ("(libev) iouring setup");
594 else
595 iouring_handle_cq (EV_A);
596 }
597 }
598
599 inline_size
600 int
601 iouring_init (EV_P_ int flags)
602 {
603 iouring_entries = IOURING_INIT_ENTRIES;
604 iouring_max_entries = 0;
605
606 if (iouring_internal_init (EV_A) < 0)
607 {
608 iouring_internal_destroy (EV_A);
609 return 0;
610 }
611
612 ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ);
613 ev_set_priority (&iouring_tfd_w, EV_MINPRI);
614 ev_io_start (EV_A_ &iouring_tfd_w);
615 ev_unref (EV_A); /* watcher should not keep loop alive */
616
617 backend_modify = iouring_modify;
618 backend_poll = iouring_poll;
619
620 return EVBACKEND_IOURING;
621 }
622
623 inline_size
624 void
625 iouring_destroy (EV_P)
626 {
627 iouring_internal_destroy (EV_A);
628 }
629