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Comparing libev/ev_linuxaio.c (file contents):
Revision 1.9 by root, Sat Jun 22 22:29:38 2019 UTC vs.
Revision 1.20 by root, Mon Jun 24 20:33:24 2019 UTC

… …
35 * and other provisions required by the GPL. If you do not delete the 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 36 * provisions above, a recipient may use your version of this file under
37 * either the BSD or the GPL. 37 * either the BSD or the GPL.
38 */ 38 */
39 39
40#define EPOLL_FALLBACK 1
41
40#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */ 42#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */
41#include <poll.h> 43#include <poll.h>
42#include <linux/aio_abi.h> 44#include <linux/aio_abi.h>
45
46#if EPOLL_FALLBACK
47# include <sys/epoll.h>
48#endif
43 49
44/* we try to fill 4kB pages exactly. 50/* we try to fill 4kB pages exactly.
45 * the ring buffer header is 32 bytes, every io event is 32 bytes. 51 * the ring buffer header is 32 bytes, every io event is 32 bytes.
46 * the kernel takes the io event number, doubles it, adds 2, adds the ring buffer. 52 * the kernel takes the io event number, doubles it, adds 2, adds the ring buffer.
47 * therefore the calculation below will use "exactly" 4kB for the ring buffer 53 * therefore the calculation below will use "exactly" 4kB for the ring buffer
48 */ 54 */
49#define EV_LINUXAIO_DEPTH (128 / 2 - 2 - 1) /* max. number of io events per batch */ 55#define EV_LINUXAIO_DEPTH (128 / 2 - 2 - 1) /* max. number of io events per batch */
50 56
51/*****************************************************************************/ 57/*****************************************************************************/
52/* syscall wrapdadoop */ 58/* syscall wrapdadoop - this section has the raw syscall definitions */
53 59
54#include <sys/syscall.h> /* no glibc wrappers */ 60#include <sys/syscall.h> /* no glibc wrappers */
55 61
56/* aio_abi.h is not versioned in any way, so we cannot test for its existance */ 62/* aio_abi.h is not versioned in any way, so we cannot test for its existance */
57#define IOCB_CMD_POLL 5 63#define IOCB_CMD_POLL 5
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74 struct io_event io_events[0]; 80 struct io_event io_events[0];
75}; 81};
76 82
77inline_size 83inline_size
78int 84int
79ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp) 85evsys_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
80{ 86{
81 return syscall (SYS_io_setup, nr_events, ctx_idp); 87 return syscall (SYS_io_setup, nr_events, ctx_idp);
82} 88}
83 89
84inline_size 90inline_size
85int 91int
86ev_io_destroy (aio_context_t ctx_id) 92evsys_io_destroy (aio_context_t ctx_id)
87{ 93{
88 return syscall (SYS_io_destroy, ctx_id); 94 return syscall (SYS_io_destroy, ctx_id);
89} 95}
90 96
91inline_size 97inline_size
92int 98int
93ev_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[]) 99evsys_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[])
94{ 100{
95 return syscall (SYS_io_submit, ctx_id, nr, cbp); 101 return syscall (SYS_io_submit, ctx_id, nr, cbp);
96} 102}
97 103
98inline_size 104inline_size
99int 105int
100ev_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result) 106evsys_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result)
101{ 107{
102 return syscall (SYS_io_cancel, ctx_id, cbp, result); 108 return syscall (SYS_io_cancel, ctx_id, cbp, result);
103} 109}
104 110
105inline_size 111inline_size
106int 112int
107ev_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout) 113evsys_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout)
108{ 114{
109 return syscall (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout); 115 return syscall (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout);
110} 116}
111 117
112/*****************************************************************************/ 118/*****************************************************************************/
… …
149linuxaio_modify (EV_P_ int fd, int oev, int nev) 155linuxaio_modify (EV_P_ int fd, int oev, int nev)
150{ 156{
151 array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp); 157 array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp);
152 struct aniocb *iocb = linuxaio_iocbps [fd]; 158 struct aniocb *iocb = linuxaio_iocbps [fd];
153 159
160#if EPOLL_FALLBACK
161 if (iocb->io.aio_reqprio < 0)
162 {
163 epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0);
164 iocb->io.aio_reqprio = 0;
165 }
166#endif
167
154 if (iocb->io.aio_buf) 168 if (iocb->io.aio_buf)
155 ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error relevant kernels */ 169 evsys_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error relevant kernels */
156 170
157 if (nev) 171 if (nev)
158 { 172 {
159 iocb->io.aio_data = fd; 173 iocb->io.aio_data = fd;
160 iocb->io.aio_fildes = fd; 174 iocb->io.aio_fildes = fd;
… …
168 array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit); 182 array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit);
169 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io; 183 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
170 } 184 }
171} 185}
172 186
187#if EPOLL_FALLBACK
188
189static void
190linuxaio_rearm_epoll (EV_P_ struct iocb *iocb, int op)
191{
192 struct epoll_event eev;
193
194 eev.events = EPOLLONESHOT;
195 if (iocb->aio_buf & POLLIN ) eev.events |= EPOLLIN ;
196 if (iocb->aio_buf & POLLOUT) eev.events |= EPOLLOUT;
197 eev.data.fd = iocb->aio_fildes;
198
199 if (epoll_ctl (backend_fd, op, iocb->aio_fildes, &eev) < 0)
200 ev_syserr ("(libeio) linuxaio epoll_ctl");
201}
202
203static void
204linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
205{
206 struct epoll_event events[16];
207
208 for (;;)
209 {
210 int idx;
211 int res = epoll_wait (backend_fd, events, sizeof (events) / sizeof (events [0]), 0);
212
213 if (expect_false (res < 0))
214 ev_syserr ("(libev) linuxaio epoll_wait");
215 else if (!res)
216 break;
217
218 for (idx = res; idx--; )
219 {
220 int fd = events [idx].data.fd;
221 uint32_t ev = events [idx].events;
222
223 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
224
225 linuxaio_rearm_epoll (EV_A_ &linuxaio_iocbps [fd]->io, EPOLL_CTL_MOD);
226
227 fd_event (EV_A_ fd,
228 (ev & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
229 | (ev & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0));
230 }
231
232 if (res < sizeof (events) / sizeof (events [0]))
233 break;
234 }
235}
236
237#endif
238
173static void 239static void
174linuxaio_parse_events (EV_P_ struct io_event *ev, int nr) 240linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
175{ 241{
176 while (nr) 242 while (nr)
177 { 243 {
178 int fd = ev->data; 244 int fd = ev->data;
179 int res = ev->res; 245 int res = ev->res;
180 246
181 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax)); 247 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
182 248
183 /* linux aio is oneshot: rearm fd */ 249 /* linux aio is oneshot: rearm fd. TODO: this does more work than needed */
184 linuxaio_iocbps [fd]->io.aio_buf = 0; 250 linuxaio_iocbps [fd]->io.aio_buf = 0;
185 anfds [fd].events = 0; 251 anfds [fd].events = 0;
186 fd_change (EV_A_ fd, 0); 252 fd_change (EV_A_ fd, 0);
187 253
188 /* feed events, we do not expect or handle POLLNVAL */ 254 /* feed events, we do not expect or handle POLLNVAL */
189 if (ecb_expect_false (res & POLLNVAL)) 255 if (expect_false (res & POLLNVAL))
190 fd_kill (EV_A_ fd); 256 fd_kill (EV_A_ fd);
191 else 257 else
192 fd_event ( 258 fd_event (
193 EV_A_ 259 EV_A_
194 fd, 260 fd,
… …
205static int 271static int
206linuxaio_get_events_from_ring (EV_P) 272linuxaio_get_events_from_ring (EV_P)
207{ 273{
208 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; 274 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
209 275
210 unsigned head = ring->head; 276 /* the kernel reads and writes both of these variables, */
277 /* as a C extension, we assume that volatile use here */
278 /* both makes reads atomic and once-only */
279 unsigned head = *(volatile unsigned *)&ring->head;
211 unsigned tail = *(volatile unsigned *)&ring->tail; 280 unsigned tail = *(volatile unsigned *)&ring->tail;
212 281
213 if (head == tail) 282 if (head == tail)
214 return 0; 283 return 0;
215 284
216 /* bail out if the ring buffer doesn't match the expected layout */ 285 /* bail out if the ring buffer doesn't match the expected layout */
217 if (ecb_expect_false (ring->magic != AIO_RING_MAGIC) 286 if (expect_false (ring->magic != AIO_RING_MAGIC)
218 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES 287 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
219 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */ 288 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
220 return 0; 289 return 0;
221 290
291 /* make sure the events up to tail are visible */
222 ECB_MEMORY_FENCE_ACQUIRE; 292 ECB_MEMORY_FENCE_ACQUIRE;
223 293
224 /* parse all available events, but only once, to avoid starvation */ 294 /* parse all available events, but only once, to avoid starvation */
225 if (tail > head) /* normal case around */ 295 if (tail > head) /* normal case around */
226 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head); 296 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
… …
228 { 298 {
229 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head); 299 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
230 linuxaio_parse_events (EV_A_ ring->io_events, tail); 300 linuxaio_parse_events (EV_A_ ring->io_events, tail);
231 } 301 }
232 302
233 ring->head = tail; 303 /* TODO: we only need a compiler barrier here, not a read fence */
304 ECB_MEMORY_FENCE_RELEASE;
305 /* as an extension to C, we hope that the volatile will make this atomic and once-only */
306 *(volatile unsigned *)&ring->head = tail;
307 /* make sure kernel can see our new head value - probably not required */
308 ECB_MEMORY_FENCE_RELEASE;
234 309
235 return 1; 310 return 1;
236} 311}
237 312
238/* read at least one event from kernel, or timeout */ 313/* read at least one event from kernel, or timeout */
239inline_size 314inline_size
240void 315void
241linuxaio_get_events (EV_P_ ev_tstamp timeout) 316linuxaio_get_events (EV_P_ ev_tstamp timeout)
242{ 317{
243 struct timespec ts; 318 struct timespec ts;
244 struct io_event ioev; 319 struct io_event ioev[1];
245 int res; 320 int res;
246 321
247 if (linuxaio_get_events_from_ring (EV_A)) 322 if (linuxaio_get_events_from_ring (EV_A))
248 return; 323 return;
249 324
250 /* no events, so wait for at least one, then poll ring buffer again */ 325 /* no events, so wait for at least one, then poll ring buffer again */
251 /* this degrades to one event per loop iteration */ 326 /* this degrades to one event per loop iteration */
252 /* if the ring buffer changes layout, but so be it */ 327 /* if the ring buffer changes layout, but so be it */
253 328
329 EV_RELEASE_CB;
330
254 ts.tv_sec = (long)timeout; 331 ts.tv_sec = (long)timeout;
255 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9); 332 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
256 333
257 res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts); 334 res = evsys_io_getevents (linuxaio_ctx, 1, sizeof (ioev) / sizeof (ioev [0]), ioev, &ts);
335
336 EV_ACQUIRE_CB;
258 337
259 if (res < 0) 338 if (res < 0)
339 if (errno == EINTR)
340 /* ignored */;
341 else
260 ev_syserr ("(libev) linuxaio io_getevents"); 342 ev_syserr ("(libev) linuxaio io_getevents");
261 else if (res) 343 else if (res)
262 { 344 {
263 /* at least one event received, handle it and any remaining ones in the ring buffer */ 345 /* at least one event received, handle it and any remaining ones in the ring buffer */
264 linuxaio_parse_events (EV_A_ &ioev, 1); 346 linuxaio_parse_events (EV_A_ ioev, res);
265 linuxaio_get_events_from_ring (EV_A); 347 linuxaio_get_events_from_ring (EV_A);
266 } 348 }
267} 349}
268 350
269static void 351static void
… …
276 /* io_submit might return less than the requested number of iocbs */ 358 /* io_submit might return less than the requested number of iocbs */
277 /* this is, afaics, only because of errors, but we go by the book and use a loop, */ 359 /* this is, afaics, only because of errors, but we go by the book and use a loop, */
278 /* which allows us to pinpoint the errornous iocb */ 360 /* which allows us to pinpoint the errornous iocb */
279 for (submitted = 0; submitted < linuxaio_submitcnt; ) 361 for (submitted = 0; submitted < linuxaio_submitcnt; )
280 { 362 {
363#if 0
364 int res;
365 if (linuxaio_submits[submitted]->aio_fildes == backend_fd)
366 res = evsys_io_submit (linuxaio_ctx, 1, linuxaio_submits + submitted);
367 else
368 { res = -1; errno = EINVAL; };
369#else
281 int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted); 370 int res = evsys_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
371#endif
282 372
283 if (ecb_expect_false (res < 0)) 373 if (expect_false (res < 0))
284 if (errno == EAGAIN) 374 if (errno == EAGAIN)
285 { 375 {
286 /* This happens when the ring buffer is full, at least. I assume this means 376 /* This happens when the ring buffer is full, at least. I assume this means
287 * that the event was queued synchronously during io_submit, and thus 377 * that the event was queued synchronously during io_submit, and thus
288 * the buffer overflowd. 378 * the buffer overflowed.
289 * In this case, we just try next loop iteration. 379 * In this case, we just try in next loop iteration.
290 * This should not result in a few fds taking priority, as the interface 380 * This should not result in a few fds taking priority, as the interface
291 * is one-shot, and we submit iocb's in a round-robin fashion. 381 * is one-shot, and we submit iocb's in a round-robin fashion.
382 * TODO: maybe make "submitted" persistent, so we don't have to memmove?
292 */ 383 */
384 if (ecb_expect_false (submitted))
385 {
293 memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits)); 386 memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits));
294 linuxaio_submitcnt -= submitted; 387 linuxaio_submitcnt -= submitted;
388 }
389
295 timeout = 0; 390 timeout = 0;
296 break; 391 break;
297 } 392 }
393#if EPOLL_FALLBACK
394 else if (errno == EINVAL)
395 {
396 /* This happens for unsupported fds, officially, but in my testing,
397 * also randomly happens for supported fds. We fall back to good old
398 * poll() here, under the assumption that this is a very rare case.
399 * See https://lore.kernel.org/patchwork/patch/1047453/ to see
400 * discussion about such a case (ttys) where polling for POLLIN
401 * fails but POLLIN|POLLOUT works.
402 */
403 struct iocb *iocb = linuxaio_submits [submitted];
404 res = 1; /* skip this iocb */
405
406 linuxaio_rearm_epoll (EV_A_ iocb, EPOLL_CTL_ADD);
407 iocb->aio_reqprio = -1; /* mark iocb as epoll */
408 }
409#endif
298 else 410 else
299 ev_syserr ("(libev) linuxaio io_submit"); 411 ev_syserr ("(libev) linuxaio io_submit");
300 412
301 submitted += res; 413 submitted += res;
302 } 414 }
… …
312int 424int
313linuxaio_init (EV_P_ int flags) 425linuxaio_init (EV_P_ int flags)
314{ 426{
315 /* would be great to have a nice test for IOCB_CMD_POLL instead */ 427 /* would be great to have a nice test for IOCB_CMD_POLL instead */
316 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */ 428 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */
317 if (ev_linux_version () < 0x041200) /* 4.18 introduced IOCB_CMD_POLL */ 429#if EPOLL_FALLBACK
430 /* 4.19 made epoll work */
431 if (ev_linux_version () < 0x041300)
318 return 0; 432 return 0;
433#else
434 /* 4.18 introduced IOCB_CMD_POLL */
435 if (ev_linux_version () < 0x041200)
436 return 0;
437#endif
319 438
320 linuxaio_ctx = 0; 439 linuxaio_ctx = 0;
321 if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0) 440 if (evsys_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
322 return 0; 441 return 0;
442
443#if EPOLL_FALLBACK
444 backend_fd = ev_epoll_create ();
445 if (backend_fd < 0)
446 {
447 evsys_io_destroy (linuxaio_ctx);
448 return 0;
449 }
450
451 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
452 ev_set_priority (&linuxaio_epoll_w, EV_MAXPRI);
453 ev_io_start (EV_A_ &linuxaio_epoll_w);
454 ev_unref (EV_A); /* watcher should not keep loop alive */
455#endif
323 456
324 backend_modify = linuxaio_modify; 457 backend_modify = linuxaio_modify;
325 backend_poll = linuxaio_poll; 458 backend_poll = linuxaio_poll;
326 459
327 linuxaio_iocbpmax = 0; 460 linuxaio_iocbpmax = 0;
… …
336 469
337inline_size 470inline_size
338void 471void
339linuxaio_destroy (EV_P) 472linuxaio_destroy (EV_P)
340{ 473{
474#if EPOLL_FALLBACK
475 close (backend_fd);
476#endif
341 linuxaio_free_iocbp (EV_A); 477 linuxaio_free_iocbp (EV_A);
342 ev_io_destroy (linuxaio_ctx); 478 ev_io_destroy (linuxaio_ctx);
343} 479}
344 480
345inline_size 481inline_size
… …
349 /* this frees all iocbs, which is very heavy-handed */ 485 /* this frees all iocbs, which is very heavy-handed */
350 linuxaio_destroy (EV_A); 486 linuxaio_destroy (EV_A);
351 linuxaio_submitcnt = 0; /* all pointers were invalidated */ 487 linuxaio_submitcnt = 0; /* all pointers were invalidated */
352 488
353 linuxaio_ctx = 0; 489 linuxaio_ctx = 0;
354 while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0) 490 while (evsys_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
355 ev_syserr ("(libev) linuxaio io_setup"); 491 ev_syserr ("(libev) linuxaio io_setup");
356 492
493#if EPOLL_FALLBACK
494 while ((backend_fd = ev_epoll_create ()) < 0)
495 ev_syserr ("(libev) linuxaio epoll_create");
496
497 ev_io_stop (EV_A_ &linuxaio_epoll_w);
498 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
499 ev_io_start (EV_A_ &linuxaio_epoll_w);
500#endif
501
357 fd_rearm_all (EV_A); 502 fd_rearm_all (EV_A);
358} 503}
359 504

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