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Comparing libev/ev_linuxaio.c (file contents):
Revision 1.15 by root, Mon Jun 24 00:04:26 2019 UTC vs.
Revision 1.34 by root, Wed Jun 26 00:01:46 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 40/*
41 * general notes about linux aio:
42 *
43 * a) at first, the linux aio IOCB_CMD_POLL functionality introduced in
44 * 4.18 looks too good to be true: both watchers and events can be
45 * batched, and events can even be handled in userspace using
46 * a ring buffer shared with the kernel. watchers can be canceled
47 * regardless of whether the fd has been closed. no problems with fork.
48 * ok, the ring buffer is 200% undocumented (there isn't even a
49 * header file), but otherwise, it's pure bliss!
50 * b) ok, watchers are one-shot, so you have to re-arm active ones
51 * on every iteration. so much for syscall-less event handling,
52 * but at least these re-arms can be batched, no big deal, right?
53 * c) well, linux as usual: the documentation lies to you: io_submit
54 * sometimes returns EINVAL because the kernel doesn't feel like
55 * handling your poll mask - ttys can be polled for POLLOUT,
56 * POLLOUT|POLLIN, but polling for POLLIN fails. just great,
57 * so we have to fall back to something else (hello, epoll),
58 * but at least the fallback can be slow, because these are
59 * exceptional cases, right?
60 * d) hmm, you have to tell the kernel the maximum number of watchers
61 * you want to queue when initialising the aio context. but of
62 * course the real limit is magically calculated in the kernel, and
63 * is often higher then we asked for. so we just have to destroy
64 * the aio context and re-create it a bit larger if we hit the limit.
65 * (starts to remind you of epoll? well, it's a bit more deterministic
66 * and less gambling, but still ugly as hell).
67 * e) that's when you find out you can also hit an arbitrary system-wide
68 * limit. or the kernel simply doesn't want to handle your watchers.
69 * what the fuck do we do then? you guessed it, in the middle
70 * of event handling we have to switch to 100% epoll polling. and
71 * that better is as fast as normal epoll polling, so you practically
72 * have to use the normal epoll backend with all its quirks.
73 * f) end result of this train wreck: it inherits all the disadvantages
74 * from epoll, while adding a number on its own. why even bother to use
75 * it? because if conditions are right and your fds are supported and you
76 * don't hit a limit, this backend is actually faster, doesn't gamble with
77 * your fds, batches watchers and events and doesn't require costly state
78 * recreates. well, until it does.
79 * g) all of this makes this backend use almost twice as much code as epoll.
80 * which in turn uses twice as much code as poll. and that#s not counting
81 * the fact that this backend also depends on the epoll backend, making
82 * it three times as much code as poll, or kqueue.
83 * h) bleah. why can't linux just do kqueue. sure kqueue is ugly, but by now
84 * it's clear that whatever linux comes up with is far, far, far worse.
85 */
41 86
42#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */ 87#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */
43#include <poll.h> 88#include <poll.h>
44#include <linux/aio_abi.h> 89#include <linux/aio_abi.h>
45 90
46#if EPOLL_FALLBACK
47# include <sys/epoll.h>
48#endif
49
50/* we try to fill 4kB pages exactly.
51 * the ring buffer header is 32 bytes, every io event is 32 bytes.
52 * the kernel takes the io event number, doubles it, adds 2, adds the ring buffer.
53 * therefore the calculation below will use "exactly" 4kB for the ring buffer
54 */
55#define EV_LINUXAIO_DEPTH (128 / 2 - 2 - 1) /* max. number of io events per batch */
56
57/*****************************************************************************/ 91/*****************************************************************************/
58/* syscall wrapdadoop */ 92/* syscall wrapdadoop - this section has the raw api/abi definitions */
59 93
60#include <sys/syscall.h> /* no glibc wrappers */ 94#include <sys/syscall.h> /* no glibc wrappers */
61 95
62/* aio_abi.h is not versioned in any way, so we cannot test for its existance */ 96/* aio_abi.h is not versioned in any way, so we cannot test for its existance */
63#define IOCB_CMD_POLL 5 97#define IOCB_CMD_POLL 5
64 98
65/* taken from linux/fs/aio.c */ 99/* taken from linux/fs/aio.c. yup, that's a .c file.
100 * not only is this totally undocumented, not even the source code
101 * can tell you what the future semantics of compat_features and
102 * incompat_features are, or what header_length actually is for.
103 */
66#define AIO_RING_MAGIC 0xa10a10a1 104#define AIO_RING_MAGIC 0xa10a10a1
67#define AIO_RING_INCOMPAT_FEATURES 0 105#define AIO_RING_INCOMPAT_FEATURES 0
68struct aio_ring 106struct aio_ring
69{ 107{
70 unsigned id; /* kernel internal index number */ 108 unsigned id; /* kernel internal index number */
… …
78 unsigned header_length; /* size of aio_ring */ 116 unsigned header_length; /* size of aio_ring */
79 117
80 struct io_event io_events[0]; 118 struct io_event io_events[0];
81}; 119};
82 120
121/*
122 * define some syscall wrappers for common architectures
123 * this is mostly for nice looks during debugging, not performance.
124 * our syscalls return < 0, not == -1, on error. which is good
125 * enough for linux aio.
126 * TODO: arm is also common nowadays, maybe even mips and x86
127 * TODO: after implementing this, it suddenly looks like overkill, but its hard to remove...
128 */
129#if __GNUC__ && __linux && ECB_AMD64 && !defined __OPTIMIZE_SIZE__
130 /* the costly errno access probably kills this for size optimisation */
131
132 #define ev_syscall(nr,narg,arg1,arg2,arg3,arg4,arg5) \
133 ({ \
134 long res; \
135 register unsigned long r5 __asm__ ("r8" ); \
136 register unsigned long r4 __asm__ ("r10"); \
137 register unsigned long r3 __asm__ ("rdx"); \
138 register unsigned long r2 __asm__ ("rsi"); \
139 register unsigned long r1 __asm__ ("rdi"); \
140 if (narg >= 5) r5 = (unsigned long)(arg5); \
141 if (narg >= 4) r4 = (unsigned long)(arg4); \
142 if (narg >= 3) r3 = (unsigned long)(arg3); \
143 if (narg >= 2) r2 = (unsigned long)(arg2); \
144 if (narg >= 1) r1 = (unsigned long)(arg1); \
145 __asm__ __volatile__ ( \
146 "syscall\n\t" \
147 : "=a" (res) \
148 : "0" (nr), "r" (r1), "r" (r2), "r" (r3), "r" (r4), "r" (r5) \
149 : "cc", "r11", "cx", "memory"); \
150 errno = -res; \
151 res; \
152 })
153
154#endif
155
156#ifdef ev_syscall
157 #define ev_syscall0(nr) ev_syscall (nr, 0, 0, 0, 0, 0, 0
158 #define ev_syscall1(nr,arg1) ev_syscall (nr, 1, arg1, 0, 0, 0, 0)
159 #define ev_syscall2(nr,arg1,arg2) ev_syscall (nr, 2, arg1, arg2, 0, 0, 0)
160 #define ev_syscall3(nr,arg1,arg2,arg3) ev_syscall (nr, 3, arg1, arg2, arg3, 0, 0)
161 #define ev_syscall4(nr,arg1,arg2,arg3,arg4) ev_syscall (nr, 3, arg1, arg2, arg3, arg4, 0)
162 #define ev_syscall5(nr,arg1,arg2,arg3,arg4,arg5) ev_syscall (nr, 5, arg1, arg2, arg3, arg4, arg5)
163#else
164 #define ev_syscall0(nr) syscall (nr)
165 #define ev_syscall1(nr,arg1) syscall (nr, arg1)
166 #define ev_syscall2(nr,arg1,arg2) syscall (nr, arg1, arg2)
167 #define ev_syscall3(nr,arg1,arg2,arg3) syscall (nr, arg1, arg2, arg3)
168 #define ev_syscall4(nr,arg1,arg2,arg3,arg4) syscall (nr, arg1, arg2, arg3, arg4)
169 #define ev_syscall5(nr,arg1,arg2,arg3,arg4,arg5) syscall (nr, arg1, arg2, arg3, arg4, arg5)
170#endif
171
83inline_size 172inline_size
84int 173int
85ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp) 174evsys_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
86{ 175{
87 return syscall (SYS_io_setup, nr_events, ctx_idp); 176 return ev_syscall2 (SYS_io_setup, nr_events, ctx_idp);
88} 177}
89 178
90inline_size 179inline_size
91int 180int
92ev_io_destroy (aio_context_t ctx_id) 181evsys_io_destroy (aio_context_t ctx_id)
93{ 182{
94 return syscall (SYS_io_destroy, ctx_id); 183 return ev_syscall1 (SYS_io_destroy, ctx_id);
95} 184}
96 185
97inline_size 186inline_size
98int 187int
99ev_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[]) 188evsys_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[])
100{ 189{
101 return syscall (SYS_io_submit, ctx_id, nr, cbp); 190 return ev_syscall3 (SYS_io_submit, ctx_id, nr, cbp);
102} 191}
103 192
104inline_size 193inline_size
105int 194int
106ev_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result) 195evsys_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result)
107{ 196{
108 return syscall (SYS_io_cancel, ctx_id, cbp, result); 197 return ev_syscall3 (SYS_io_cancel, ctx_id, cbp, result);
109} 198}
110 199
111inline_size 200inline_size
112int 201int
113ev_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout) 202evsys_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout)
114{ 203{
115 return syscall (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout); 204 return ev_syscall5 (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout);
116} 205}
117 206
118/*****************************************************************************/ 207/*****************************************************************************/
119/* actual backed implementation */ 208/* actual backed implementation */
120 209
210ecb_cold
211static int
212linuxaio_nr_events (EV_P)
213{
214 /* we start with 16 iocbs and incraese from there
215 * that's tiny, but the kernel has a rather low system-wide
216 * limit that can be reached quickly, so let's be parsimonious
217 * with this resource.
218 * Rest assured, the kernel generously rounds up small and big numbers
219 * in different ways (but doesn't seem to charge you for it).
220 * The 15 here is because the kernel usually has a power of two as aio-max-nr,
221 * and this helps to take advantage of that limit.
222 */
223
224 /* we try to fill 4kB pages exactly.
225 * the ring buffer header is 32 bytes, every io event is 32 bytes.
226 * the kernel takes the io requests number, doubles it, adds 2
227 * and adds the ring buffer.
228 * the way we use this is by starting low, and then roughly doubling the
229 * size each time we hit a limit.
230 */
231
232 int requests = 15 << linuxaio_iteration;
233 int one_page = (4096
234 / sizeof (struct io_event) ) / 2; /* how many fit into one page */
235 int first_page = ((4096 - sizeof (struct aio_ring))
236 / sizeof (struct io_event) - 2) / 2; /* how many fit into the first page */
237
238 /* if everything fits into one page, use count exactly */
239 if (requests > first_page)
240 /* otherwise, round down to full pages and add the first page */
241 requests = requests / one_page * one_page + first_page;
242
243 return requests;
244}
245
121/* we use out own wrapper structure in acse we ever want to do something "clever" */ 246/* we use out own wrapper structure in case we ever want to do something "clever" */
122typedef struct aniocb 247typedef struct aniocb
123{ 248{
124 struct iocb io; 249 struct iocb io;
125 /*int inuse;*/ 250 /*int inuse;*/
126} *ANIOCBP; 251} *ANIOCBP;
127 252
128inline_size 253inline_size
129void 254void
130linuxaio_array_needsize_iocbp (ANIOCBP *base, int count) 255linuxaio_array_needsize_iocbp (ANIOCBP *base, int offset, int count)
131{ 256{
132 /* TODO: quite the overhead to allocate every iocb separately, maybe use our own alocator? */
133 while (count--) 257 while (count--)
134 { 258 {
259 /* TODO: quite the overhead to allocate every iocb separately, maybe use our own allocator? */
135 *base = (ANIOCBP)ev_malloc (sizeof (**base)); 260 ANIOCBP iocb = (ANIOCBP)ev_malloc (sizeof (*iocb));
136 /* TODO: full zero initialize required? */ 261
262 /* full zero initialise is probably not required at the moment, but
263 * this is not well documented, so we better do it.
264 */
137 memset (*base, 0, sizeof (**base)); 265 memset (iocb, 0, sizeof (*iocb));
138 /* would be nice to initialize fd/data as well, but array_needsize API doesn't support that */ 266
139 (*base)->io.aio_lio_opcode = IOCB_CMD_POLL; 267 iocb->io.aio_lio_opcode = IOCB_CMD_POLL;
140 ++base; 268 iocb->io.aio_data = offset;
269 iocb->io.aio_fildes = offset;
270
271 base [offset++] = iocb;
141 } 272 }
142} 273}
143 274
144ecb_cold 275ecb_cold
145static void 276static void
… …
153 284
154static void 285static void
155linuxaio_modify (EV_P_ int fd, int oev, int nev) 286linuxaio_modify (EV_P_ int fd, int oev, int nev)
156{ 287{
157 array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp); 288 array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp);
158 struct aniocb *iocb = linuxaio_iocbps [fd]; 289 ANIOCBP iocb = linuxaio_iocbps [fd];
159 290
160#if EPOLL_FALLBACK
161 if (iocb->io.aio_reqprio < 0) 291 if (iocb->io.aio_reqprio < 0)
162 { 292 {
293 /* we handed this fd over to epoll, so undo this first */
294 /* we do it manually because the optimisations on epoll_modify won't do us any good */
163 epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0); 295 epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0);
296 anfds [fd].emask = 0;
164 iocb->io.aio_reqprio = 0; 297 iocb->io.aio_reqprio = 0;
165 } 298 }
166#endif
167 299
168 if (iocb->io.aio_buf) 300 if (iocb->io.aio_buf)
169 ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error relevant kernels */ 301 {
302 evsys_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0);
303 /* on relevant kernels, io_cancel fails with EINPROGRES if everything is fine */
304 assert (("libev: linuxaio unexpected io_cancel failed", errno != EINPROGRESS));
305 }
170 306
171 if (nev) 307 if (nev)
172 { 308 {
173 iocb->io.aio_data = fd;
174 iocb->io.aio_fildes = fd;
175 iocb->io.aio_buf = 309 iocb->io.aio_buf =
176 (nev & EV_READ ? POLLIN : 0) 310 (nev & EV_READ ? POLLIN : 0)
177 | (nev & EV_WRITE ? POLLOUT : 0); 311 | (nev & EV_WRITE ? POLLOUT : 0);
178 312
179 /* queue iocb up for io_submit */ 313 /* queue iocb up for io_submit */
180 /* this assumes we only ever get one call per fd per loop iteration */ 314 /* this assumes we only ever get one call per fd per loop iteration */
… …
183 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io; 317 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
184 } 318 }
185} 319}
186 320
187static void 321static void
322linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
323{
324 epoll_poll (EV_A_ 0);
325}
326
327static void
328linuxaio_fd_rearm (EV_P_ int fd)
329{
330 anfds [fd].events = 0;
331 linuxaio_iocbps [fd]->io.aio_buf = 0;
332 fd_change (EV_A_ fd, EV_ANFD_REIFY);
333}
334
335static void
188linuxaio_parse_events (EV_P_ struct io_event *ev, int nr) 336linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
189{ 337{
190 while (nr) 338 while (nr)
191 { 339 {
192 int fd = ev->data; 340 int fd = ev->data;
193 int res = ev->res; 341 int res = ev->res;
194 342
195 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax)); 343 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
196 344
197 /* linux aio is oneshot: rearm fd */
198 linuxaio_iocbps [fd]->io.aio_buf = 0;
199 anfds [fd].events = 0;
200 fd_change (EV_A_ fd, 0);
201
202 /* feed events, we do not expect or handle POLLNVAL */ 345 /* feed events, we do not expect or handle POLLNVAL */
203 if (ecb_expect_false (res & POLLNVAL))
204 fd_kill (EV_A_ fd);
205 else
206 fd_event ( 346 fd_event (
207 EV_A_ 347 EV_A_
208 fd, 348 fd,
209 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) 349 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
210 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) 350 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
211 ); 351 );
352
353 /* linux aio is oneshot: rearm fd. TODO: this does more work than needed */
354 linuxaio_fd_rearm (EV_A_ fd);
212 355
213 --nr; 356 --nr;
214 ++ev; 357 ++ev;
215 } 358 }
216} 359}
217 360
218/* get any events from ringbuffer, return true if any were handled */ 361/* get any events from ring buffer, return true if any were handled */
219static int 362static int
220linuxaio_get_events_from_ring (EV_P) 363linuxaio_get_events_from_ring (EV_P)
221{ 364{
222 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; 365 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
223 366
… …
229 372
230 if (head == tail) 373 if (head == tail)
231 return 0; 374 return 0;
232 375
233 /* bail out if the ring buffer doesn't match the expected layout */ 376 /* bail out if the ring buffer doesn't match the expected layout */
234 if (ecb_expect_false (ring->magic != AIO_RING_MAGIC) 377 if (expect_false (ring->magic != AIO_RING_MAGIC)
235 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES 378 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
236 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */ 379 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
237 return 0; 380 return 0;
238 381
239 /* make sure the events up to tail are visible */ 382 /* make sure the events up to tail are visible */
240 ECB_MEMORY_FENCE_ACQUIRE; 383 ECB_MEMORY_FENCE_ACQUIRE;
241 384
… …
246 { 389 {
247 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head); 390 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
248 linuxaio_parse_events (EV_A_ ring->io_events, tail); 391 linuxaio_parse_events (EV_A_ ring->io_events, tail);
249 } 392 }
250 393
394 ECB_MEMORY_FENCE_RELEASE;
251 /* as an extension to C, we hope that the volatile will makethis atomic and once-only */ 395 /* as an extension to C, we hope that the volatile will make this atomic and once-only */
252 *(volatile unsigned *)&ring->head = tail; 396 *(volatile unsigned *)&ring->head = tail;
253 /* make sure kernel can see our new head value - probably not required */
254 ECB_MEMORY_FENCE_RELEASE;
255 397
256 return 1; 398 return 1;
257} 399}
258 400
259/* read at least one event from kernel, or timeout */ 401/* read at least one event from kernel, or timeout */
260inline_size 402inline_size
261void 403void
262linuxaio_get_events (EV_P_ ev_tstamp timeout) 404linuxaio_get_events (EV_P_ ev_tstamp timeout)
263{ 405{
264 struct timespec ts; 406 struct timespec ts;
265 struct io_event ioev; 407 struct io_event ioev[1];
266 int res; 408 int res;
267 409
268 if (linuxaio_get_events_from_ring (EV_A)) 410 if (linuxaio_get_events_from_ring (EV_A))
269 return; 411 return;
270 412
271 /* no events, so wait for at least one, then poll ring buffer again */ 413 /* no events, so wait for at least one, then poll ring buffer again */
272 /* this degrades to one event per loop iteration */ 414 /* this degrades to one event per loop iteration */
273 /* if the ring buffer changes layout, but so be it */ 415 /* if the ring buffer changes layout, but so be it */
274 416
417 EV_RELEASE_CB;
418
275 ts.tv_sec = (long)timeout; 419 ts.tv_sec = (long)timeout;
276 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9); 420 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
277 421
278 res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts); 422 res = evsys_io_getevents (linuxaio_ctx, 1, sizeof (ioev) / sizeof (ioev [0]), ioev, &ts);
423
424 EV_ACQUIRE_CB;
279 425
280 if (res < 0) 426 if (res < 0)
281 if (errno == EINTR) 427 if (errno == EINTR)
282 /* ignored */; 428 /* ignored */;
283 else 429 else
284 ev_syserr ("(libev) linuxaio io_getevents"); 430 ev_syserr ("(libev) linuxaio io_getevents");
285 else if (res) 431 else if (res)
286 { 432 {
287 /* at least one event received, handle it and any remaining ones in the ring buffer */ 433 /* at least one event available, handle it and any remaining ones in the ring buffer */
288 linuxaio_parse_events (EV_A_ &ioev, 1); 434 linuxaio_parse_events (EV_A_ ioev, res);
289 linuxaio_get_events_from_ring (EV_A); 435 linuxaio_get_events_from_ring (EV_A);
290 } 436 }
291} 437}
292 438
293#if EPOLL_FALLBACK 439inline_size
294static void 440int
295linuxaio_rearm_epoll (EV_P_ struct iocb *iocb, int op) 441linuxaio_io_setup (EV_P)
296{ 442{
297 struct epoll_event eev; 443 linuxaio_ctx = 0;
298 444 return evsys_io_setup (linuxaio_nr_events (EV_A), &linuxaio_ctx);
299 eev.events = EPOLLONESHOT;
300 if (iocb->aio_buf & POLLIN ) eev.events |= EPOLLIN ;
301 if (iocb->aio_buf & POLLOUT) eev.events |= EPOLLOUT;
302 eev.data.fd = iocb->aio_fildes;
303
304 if (epoll_ctl (backend_fd, op, iocb->aio_fildes, &eev) < 0)
305 ev_syserr ("(libeio) linuxaio epoll_ctl");
306} 445}
307#endif
308 446
309static void 447static void
310linuxaio_poll (EV_P_ ev_tstamp timeout) 448linuxaio_poll (EV_P_ ev_tstamp timeout)
311{ 449{
312 int submitted; 450 int submitted;
313 451
314 /* first phase: submit new iocbs */ 452 /* first phase: submit new iocbs */
315 453
316 /* io_submit might return less than the requested number of iocbs */ 454 /* io_submit might return less than the requested number of iocbs */
317 /* this is, afaics, only because of errors, but we go by the book and use a loop, */ 455 /* this is, afaics, only because of errors, but we go by the book and use a loop, */
318 /* which allows us to pinpoint the errornous iocb */ 456 /* which allows us to pinpoint the erroneous iocb */
319 for (submitted = 0; submitted < linuxaio_submitcnt; ) 457 for (submitted = 0; submitted < linuxaio_submitcnt; )
320 { 458 {
321 int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted); 459 int res = evsys_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
322 460
323 if (ecb_expect_false (res < 0)) 461 if (expect_false (res < 0))
324 if (errno == EAGAIN)
325 {
326 /* This happens when the ring buffer is full, at least. I assume this means
327 * that the event was queued synchronously during io_submit, and thus
328 * the buffer overflowed.
329 * In this case, we just try in next loop iteration.
330 * This should not result in a few fds taking priority, as the interface
331 * is one-shot, and we submit iocb's in a round-robin fashion.
332 */
333 memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits));
334 linuxaio_submitcnt -= submitted;
335 timeout = 0;
336 break;
337 }
338#if EPOLL_FALLBACK
339 else if (errno == EINVAL) 462 if (errno == EINVAL)
340 { 463 {
341 /* This happens for unsupported fds, officially, but in my testing, 464 /* This happens for unsupported fds, officially, but in my testing,
342 * also randomly happens for supported fds. We fall back to good old 465 * also randomly happens for supported fds. We fall back to good old
343 * poll() here, under the assumption that this is a very rare case. 466 * poll() here, under the assumption that this is a very rare case.
344 * See https://lore.kernel.org/patchwork/patch/1047453/ for evidence 467 * See https://lore.kernel.org/patchwork/patch/1047453/ to see
345 * that the problem is known, but ignored. 468 * discussion about such a case (ttys) where polling for POLLIN
469 * fails but POLLIN|POLLOUT works.
346 */ 470 */
347 struct iocb *iocb = linuxaio_submits [submitted]; 471 struct iocb *iocb = linuxaio_submits [submitted];
472 epoll_modify (EV_A_ iocb->aio_fildes, 0, anfds [iocb->aio_fildes].events);
473 iocb->aio_reqprio = -1; /* mark iocb as epoll */
474
475 res = 1; /* skip this iocb - another iocb, another chance */
476 }
477 else if (errno == EAGAIN)
478 {
479 /* This happens when the ring buffer is full, or some other shit we
480 * don't know and isn't documented. Most likely because we have too
481 * many requests and linux aio can't be assed to handle them.
482 * In this case, we try to allocate a larger ring buffer, freeing
483 * ours first. This might fail, in which case we have to fall back to 100%
484 * epoll.
485 * God, how I hate linux not getting its act together. Ever.
486 */
487 evsys_io_destroy (linuxaio_ctx);
488 linuxaio_submitcnt = 0;
489
490 /* rearm all fds with active iocbs */
491 {
492 int fd;
493 for (fd = 0; fd < linuxaio_iocbpmax; ++fd)
494 if (linuxaio_iocbps [fd]->io.aio_buf)
495 linuxaio_fd_rearm (EV_A_ fd);
496 }
497
498 ++linuxaio_iteration;
499 if (linuxaio_io_setup (EV_A) < 0)
500 {
501 /* to bad, we can't get a new aio context, go 100% epoll */
502 linuxaio_free_iocbp (EV_A);
503 ev_io_stop (EV_A_ &linuxaio_epoll_w);
504 ev_ref (EV_A);
505 linuxaio_ctx = 0;
506 backend_modify = epoll_modify;
507 backend_poll = epoll_poll;
508 }
509
510 timeout = 0;
511 /* it's easiest to handle this mess in another iteration */
512 return;
513 }
514 else if (errno == EBADF)
515 {
516 assert (("libev: event loop rejected bad fd", errno != EBADF));
517 fd_kill (EV_A_ linuxaio_submits [submitted]->aio_fildes);
518
348 res = 1; /* skip this iocb */ 519 res = 1; /* skip this iocb */
349
350 linuxaio_rearm_epoll (EV_A_ iocb, EPOLL_CTL_ADD);
351 iocb->aio_reqprio = -1; /* mark iocb as epoll */
352 } 520 }
353#endif
354 else 521 else
355 ev_syserr ("(libev) linuxaio io_submit"); 522 ev_syserr ("(libev) linuxaio io_submit");
356 523
357 submitted += res; 524 submitted += res;
358 } 525 }
… …
362 /* second phase: fetch and parse events */ 529 /* second phase: fetch and parse events */
363 530
364 linuxaio_get_events (EV_A_ timeout); 531 linuxaio_get_events (EV_A_ timeout);
365} 532}
366 533
367#if EPOLL_FALLBACK
368
369static void
370linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
371{
372 struct epoll_event events[16];
373
374 for (;;)
375 {
376 int idx;
377 int res = epoll_wait (backend_fd, events, sizeof (events) / sizeof (events [0]), 0);
378
379 if (ecb_expect_false (res < 0))
380 ev_syserr ("(libev) linuxaio epoll_wait");
381 else if (!res)
382 break;
383
384 for (idx = res; idx--; )
385 {
386 int fd = events [idx].data.fd;
387 uint32_t ev = events [idx].events;
388
389 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
390
391 linuxaio_rearm_epoll (EV_A_ &linuxaio_iocbps [fd]->io, EPOLL_CTL_MOD);
392
393 fd_event (EV_A_ fd,
394 (ev & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
395 | (ev & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0));
396 }
397
398 if (res < sizeof (events) / sizeof (events [0]))
399 break;
400 }
401}
402
403#endif
404
405inline_size 534inline_size
406int 535int
407linuxaio_init (EV_P_ int flags) 536linuxaio_init (EV_P_ int flags)
408{ 537{
409 /* would be great to have a nice test for IOCB_CMD_POLL instead */ 538 /* would be great to have a nice test for IOCB_CMD_POLL instead */
410 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */ 539 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */
411#if EPOLL_FALLBACK 540 /* 4.18 introduced IOCB_CMD_POLL, 4.19 made epoll work, and we need that */
412 /* 4.19 made epoll work */
413 if (ev_linux_version () < 0x041300) 541 if (ev_linux_version () < 0x041300)
414 return 0; 542 return 0;
415#else 543
416 /* 4.18 introduced IOCB_CMD_POLL */ 544 if (!epoll_init (EV_A_ 0))
417 if (ev_linux_version () < 0x041200)
418 return 0; 545 return 0;
419#endif
420 546
421 linuxaio_ctx = 0; 547 linuxaio_iteration = 0;
422 if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
423 return 0;
424 548
425#if EPOLL_FALLBACK 549 if (linuxaio_io_setup (EV_A) < 0)
426 backend_fd = ev_epoll_create ();
427 if (backend_fd < 0)
428 { 550 {
429 ev_io_destroy (linuxaio_ctx); 551 epoll_destroy (EV_A);
430 return 0; 552 return 0;
431 } 553 }
432 554
433 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ); 555 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
556 ev_set_priority (&linuxaio_epoll_w, EV_MAXPRI);
434 ev_io_start (EV_A_ &linuxaio_epoll_w); 557 ev_io_start (EV_A_ &linuxaio_epoll_w);
435 ev_unref (EV_A); /* watcher should not keep loop alive */ 558 ev_unref (EV_A); /* watcher should not keep loop alive */
436#endif
437 559
438 backend_modify = linuxaio_modify; 560 backend_modify = linuxaio_modify;
439 backend_poll = linuxaio_poll; 561 backend_poll = linuxaio_poll;
440 562
441 linuxaio_iocbpmax = 0; 563 linuxaio_iocbpmax = 0;
… …
450 572
451inline_size 573inline_size
452void 574void
453linuxaio_destroy (EV_P) 575linuxaio_destroy (EV_P)
454{ 576{
455#if EPOLL_FALLBACK 577 epoll_destroy (EV_A);
456 close (backend_fd);
457#endif
458 linuxaio_free_iocbp (EV_A); 578 linuxaio_free_iocbp (EV_A);
459 ev_io_destroy (linuxaio_ctx); 579 evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */
460} 580}
461 581
462inline_size 582inline_size
463void 583void
464linuxaio_fork (EV_P) 584linuxaio_fork (EV_P)
465{ 585{
466 /* this frees all iocbs, which is very heavy-handed */ 586 /* this frees all iocbs, which is very heavy-handed */
467 linuxaio_destroy (EV_A); 587 linuxaio_destroy (EV_A);
468 linuxaio_submitcnt = 0; /* all pointers were invalidated */ 588 linuxaio_submitcnt = 0; /* all pointers were invalidated */
469 589
470 linuxaio_ctx = 0; 590 linuxaio_iteration = 0; /* we start over in the child */
471 while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0) 591
592 while (linuxaio_io_setup (EV_A) < 0)
472 ev_syserr ("(libev) linuxaio io_setup"); 593 ev_syserr ("(libev) linuxaio io_setup");
473 594
474#if EPOLL_FALLBACK 595 /* forking epoll should also effectively unregister all fds from the backend */
475 while ((backend_fd = ev_epoll_create ()) < 0) 596 epoll_fork (EV_A);
476 ev_syserr ("(libev) linuxaio epoll_create");
477 597
478 ev_io_stop (EV_A_ &linuxaio_epoll_w); 598 ev_io_stop (EV_A_ &linuxaio_epoll_w);
479 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ); 599 ev_io_set (EV_A_ &linuxaio_epoll_w, backend_fd, EV_READ);
480 ev_io_start (EV_A_ &linuxaio_epoll_w); 600 ev_io_start (EV_A_ &linuxaio_epoll_w);
481#endif
482 601
602 /* epoll_fork already did this. hopefully */
483 fd_rearm_all (EV_A); 603 /*fd_rearm_all (EV_A);*/
484} 604}
485 605

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