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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 1.40 by root, Mon Jul 1 20:35:17 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/*
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 */
86
40#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 */
41#include <poll.h> 88#include <poll.h>
42#include <linux/aio_abi.h> 89#include <linux/aio_abi.h>
43 90
44/* we try to fill 4kB pages exactly.
45 * 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.
47 * therefore the calculation below will use "exactly" 4kB for the ring buffer
48 */
49#define EV_LINUXAIO_DEPTH (128 / 2 - 2 - 1) /* max. number of io events per batch */
50
51/*****************************************************************************/ 91/*****************************************************************************/
52/* syscall wrapdadoop */ 92/* syscall wrapdadoop - this section has the raw api/abi definitions */
53 93
54#include <sys/syscall.h> /* no glibc wrappers */ 94#include <sys/syscall.h> /* no glibc wrappers */
55 95
56/* 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 */
57#define IOCB_CMD_POLL 5 97#define IOCB_CMD_POLL 5
58 98
59/* 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 */
60#define AIO_RING_MAGIC 0xa10a10a1 104#define AIO_RING_MAGIC 0xa10a10a1
61#define AIO_RING_INCOMPAT_FEATURES 0 105#define EV_AIO_RING_INCOMPAT_FEATURES 0
62struct aio_ring 106struct aio_ring
63{ 107{
64 unsigned id; /* kernel internal index number */ 108 unsigned id; /* kernel internal index number */
65 unsigned nr; /* number of io_events */ 109 unsigned nr; /* number of io_events */
66 unsigned head; /* Written to by userland or by kernel. */ 110 unsigned head; /* Written to by userland or by kernel. */
… …
72 unsigned header_length; /* size of aio_ring */ 116 unsigned header_length; /* size of aio_ring */
73 117
74 struct io_event io_events[0]; 118 struct io_event io_events[0];
75}; 119};
76 120
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
77inline_size 172inline_size
78int 173int
79ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp) 174evsys_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
80{ 175{
81 return syscall (SYS_io_setup, nr_events, ctx_idp); 176 return ev_syscall2 (SYS_io_setup, nr_events, ctx_idp);
82} 177}
83 178
84inline_size 179inline_size
85int 180int
86ev_io_destroy (aio_context_t ctx_id) 181evsys_io_destroy (aio_context_t ctx_id)
87{ 182{
88 return syscall (SYS_io_destroy, ctx_id); 183 return ev_syscall1 (SYS_io_destroy, ctx_id);
89} 184}
90 185
91inline_size 186inline_size
92int 187int
93ev_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[])
94{ 189{
95 return syscall (SYS_io_submit, ctx_id, nr, cbp); 190 return ev_syscall3 (SYS_io_submit, ctx_id, nr, cbp);
96} 191}
97 192
98inline_size 193inline_size
99int 194int
100ev_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)
101{ 196{
102 return syscall (SYS_io_cancel, ctx_id, cbp, result); 197 return ev_syscall3 (SYS_io_cancel, ctx_id, cbp, result);
103} 198}
104 199
105inline_size 200inline_size
106int 201int
107ev_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)
108{ 203{
109 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);
110} 205}
111 206
112/*****************************************************************************/ 207/*****************************************************************************/
113/* actual backed implementation */ 208/* actual backed implementation */
114 209
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
115/* 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" */
116typedef struct aniocb 247typedef struct aniocb
117{ 248{
118 struct iocb io; 249 struct iocb io;
119 /*int inuse;*/ 250 /*int inuse;*/
120} *ANIOCBP; 251} *ANIOCBP;
121 252
122inline_size 253inline_size
123void 254void
124linuxaio_array_needsize_iocbp (ANIOCBP *base, int count) 255linuxaio_array_needsize_iocbp (ANIOCBP *base, int offset, int count)
125{ 256{
126 /* TODO: quite the overhead to allocate every iocb separately, maybe use our own alocator? */
127 while (count--) 257 while (count--)
128 { 258 {
259 /* TODO: quite the overhead to allocate every iocb separately, maybe use our own allocator? */
129 *base = (ANIOCBP)ev_malloc (sizeof (**base)); 260 ANIOCBP iocb = (ANIOCBP)ev_malloc (sizeof (*iocb));
130 /* 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 */
131 memset (*base, 0, sizeof (**base)); 265 memset (iocb, 0, sizeof (*iocb));
132 /* would be nice to initialize fd/data as well, but array_needsize API doesn't support that */ 266
133 (*base)->io.aio_lio_opcode = IOCB_CMD_POLL; 267 iocb->io.aio_lio_opcode = IOCB_CMD_POLL;
134 ++base; 268 iocb->io.aio_data = offset;
269 iocb->io.aio_fildes = offset;
270
271 base [offset++] = iocb;
135 } 272 }
136} 273}
137 274
138ecb_cold 275ecb_cold
139static void 276static void
… …
147 284
148static void 285static void
149linuxaio_modify (EV_P_ int fd, int oev, int nev) 286linuxaio_modify (EV_P_ int fd, int oev, int nev)
150{ 287{
151 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);
152 struct aniocb *iocb = linuxaio_iocbps [fd]; 289 ANIOCBP iocb = linuxaio_iocbps [fd];
290
291 if (iocb->io.aio_reqprio < 0)
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 */
295 epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0);
296 anfds [fd].emask = 0;
297 iocb->io.aio_reqprio = 0;
298 }
153 299
154 if (iocb->io.aio_buf) 300 if (iocb->io.aio_buf)
155 ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error relevant kernels */ 301 {
302 for (;;)
303 {
304 /* on all relevant kernels, io_cancel fails with EINPROGRESS on "success" */
305 if (expect_false (evsys_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0) == 0))
306 break;
307
308 if (expect_true (errno == EINPROGRESS))
309 break;
310
311 /* the EINPROGRESS test is for nicer error message. clumsy. */
312 assert (("libev: linuxaio unexpected io_cancel failed", errno != EINPROGRESS && errno != EINTR));
313 }
314 }
156 315
157 if (nev) 316 if (nev)
158 { 317 {
159 iocb->io.aio_data = fd;
160 iocb->io.aio_fildes = fd;
161 iocb->io.aio_buf = 318 iocb->io.aio_buf =
162 (nev & EV_READ ? POLLIN : 0) 319 (nev & EV_READ ? POLLIN : 0)
163 | (nev & EV_WRITE ? POLLOUT : 0); 320 | (nev & EV_WRITE ? POLLOUT : 0);
164 321
165 /* queue iocb up for io_submit */ 322 /* queue iocb up for io_submit */
166 /* this assumes we only ever get one call per fd per loop iteration */ 323 /* this assumes we only ever get one call per fd per loop iteration */
… …
169 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io; 326 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
170 } 327 }
171} 328}
172 329
173static void 330static void
331linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
332{
333 epoll_poll (EV_A_ 0);
334}
335
336inline_speed
337void
338linuxaio_fd_rearm (EV_P_ int fd)
339{
340 anfds [fd].events = 0;
341 linuxaio_iocbps [fd]->io.aio_buf = 0;
342 fd_change (EV_A_ fd, EV_ANFD_REIFY);
343}
344
345static void
174linuxaio_parse_events (EV_P_ struct io_event *ev, int nr) 346linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
175{ 347{
176 while (nr) 348 while (nr)
177 { 349 {
178 int fd = ev->data; 350 int fd = ev->data;
179 int res = ev->res; 351 int res = ev->res;
180 352
181 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax)); 353 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
182 354
183 /* linux aio is oneshot: rearm fd */
184 linuxaio_iocbps [fd]->io.aio_buf = 0;
185 anfds [fd].events = 0;
186 fd_change (EV_A_ fd, 0);
187
188 /* feed events, we do not expect or handle POLLNVAL */ 355 /* feed events, we do not expect or handle POLLNVAL */
189 if (ecb_expect_false (res & POLLNVAL))
190 fd_kill (EV_A_ fd);
191 else
192 fd_event ( 356 fd_event (
193 EV_A_ 357 EV_A_
194 fd, 358 fd,
195 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) 359 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
196 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) 360 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
197 ); 361 );
362
363 /* linux aio is oneshot: rearm fd. TODO: this does more work than strictly needed */
364 linuxaio_fd_rearm (EV_A_ fd);
198 365
199 --nr; 366 --nr;
200 ++ev; 367 ++ev;
201 } 368 }
202} 369}
203 370
204/* get any events from ringbuffer, return true if any were handled */ 371/* get any events from ring buffer, return true if any were handled */
205static int 372static int
206linuxaio_get_events_from_ring (EV_P) 373linuxaio_get_events_from_ring (EV_P)
207{ 374{
208 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; 375 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
209 376
210 unsigned head = ring->head; 377 /* the kernel reads and writes both of these variables, */
378 /* as a C extension, we assume that volatile use here */
379 /* both makes reads atomic and once-only */
380 unsigned head = *(volatile unsigned *)&ring->head;
211 unsigned tail = *(volatile unsigned *)&ring->tail; 381 unsigned tail = *(volatile unsigned *)&ring->tail;
212 382
213 if (head == tail) 383 if (head == tail)
214 return 0; 384 return 0;
215 385
216 /* bail out if the ring buffer doesn't match the expected layout */ 386 /* make sure the events up to tail are visible */
217 if (ecb_expect_false (ring->magic != AIO_RING_MAGIC)
218 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
219 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
220 return 0;
221
222 ECB_MEMORY_FENCE_ACQUIRE; 387 ECB_MEMORY_FENCE_ACQUIRE;
223 388
224 /* parse all available events, but only once, to avoid starvation */ 389 /* parse all available events, but only once, to avoid starvation */
225 if (tail > head) /* normal case around */ 390 if (tail > head) /* normal case around */
226 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head); 391 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
… …
228 { 393 {
229 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head); 394 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
230 linuxaio_parse_events (EV_A_ ring->io_events, tail); 395 linuxaio_parse_events (EV_A_ ring->io_events, tail);
231 } 396 }
232 397
233 ring->head = tail; 398 ECB_MEMORY_FENCE_RELEASE;
399 /* as an extension to C, we hope that the volatile will make this atomic and once-only */
400 *(volatile unsigned *)&ring->head = tail;
234 401
235 return 1; 402 return 1;
403}
404
405inline_size
406int
407linuxaio_ringbuf_valid (EV_P)
408{
409 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
410
411 return expect_true (ring->magic == AIO_RING_MAGIC)
412 && ring->incompat_features == EV_AIO_RING_INCOMPAT_FEATURES
413 && ring->header_length == sizeof (struct aio_ring); /* TODO: or use it to find io_event[0]? */
236} 414}
237 415
238/* read at least one event from kernel, or timeout */ 416/* read at least one event from kernel, or timeout */
239inline_size 417inline_size
240void 418void
241linuxaio_get_events (EV_P_ ev_tstamp timeout) 419linuxaio_get_events (EV_P_ ev_tstamp timeout)
242{ 420{
243 struct timespec ts; 421 struct timespec ts;
244 struct io_event ioev; 422 struct io_event ioev[8]; /* 256 octet stack space */
245 int res; 423 int want = 1; /* how many events to request */
424 int ringbuf_valid = linuxaio_ringbuf_valid (EV_A);
246 425
426 if (expect_true (ringbuf_valid))
427 {
428 /* if the ring buffer has any events, we don't wait or call the kernel at all */
247 if (linuxaio_get_events_from_ring (EV_A)) 429 if (linuxaio_get_events_from_ring (EV_A))
248 return; 430 return;
249 431
250 /* no events, so wait for at least one, then poll ring buffer again */ 432 /* if the ring buffer is empty, and we don't have a timeout, then don't call the kernel */
251 /* this degrades to one event per loop iteration */ 433 if (!timeout)
252 /* if the ring buffer changes layout, but so be it */ 434 return;
435 }
436 else
437 /* no ringbuffer, request slightly larger batch */
438 want = sizeof (ioev) / sizeof (ioev [0]);
253 439
440 /* no events, so wait for some
441 * for fairness reasons, we do this in a loop, to fetch all events
442 */
443 for (;;)
444 {
445 int res;
446
447 EV_RELEASE_CB;
448
254 ts.tv_sec = (long)timeout; 449 ts.tv_sec = (long)timeout;
255 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9); 450 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
256 451
257 res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts); 452 res = evsys_io_getevents (linuxaio_ctx, 1, want, ioev, &ts);
258 453
454 EV_ACQUIRE_CB;
455
259 if (res < 0) 456 if (res < 0)
457 if (errno == EINTR)
458 /* ignored, retry */;
459 else
260 ev_syserr ("(libev) linuxaio io_getevents"); 460 ev_syserr ("(libev) linuxaio io_getevents");
261 else if (res) 461 else if (res)
262 { 462 {
263 /* at least one event received, handle it and any remaining ones in the ring buffer */ 463 /* at least one event available, handle them */
264 linuxaio_parse_events (EV_A_ &ioev, 1); 464 linuxaio_parse_events (EV_A_ ioev, res);
465
466 if (expect_true (ringbuf_valid))
467 {
468 /* if we have a ring buffer, handle any remaining events in it */
265 linuxaio_get_events_from_ring (EV_A); 469 linuxaio_get_events_from_ring (EV_A);
470
471 /* at this point, we should have handled all outstanding events */
472 break;
473 }
474 else if (res < want)
475 /* otherwise, if there were fewere events than we wanted, we assume there are no more */
476 break;
477 }
478 else
479 break; /* no events from the kernel, we are done */
480
481 timeout = 0; /* only wait in the first iteration */
266 } 482 }
483}
484
485inline_size
486int
487linuxaio_io_setup (EV_P)
488{
489 linuxaio_ctx = 0;
490 return evsys_io_setup (linuxaio_nr_events (EV_A), &linuxaio_ctx);
267} 491}
268 492
269static void 493static void
270linuxaio_poll (EV_P_ ev_tstamp timeout) 494linuxaio_poll (EV_P_ ev_tstamp timeout)
271{ 495{
… …
273 497
274 /* first phase: submit new iocbs */ 498 /* first phase: submit new iocbs */
275 499
276 /* io_submit might return less than the requested number of iocbs */ 500 /* 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, */ 501 /* 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 */ 502 /* which allows us to pinpoint the erroneous iocb */
279 for (submitted = 0; submitted < linuxaio_submitcnt; ) 503 for (submitted = 0; submitted < linuxaio_submitcnt; )
280 { 504 {
281 int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted); 505 int res = evsys_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
282 506
283 if (ecb_expect_false (res < 0)) 507 if (expect_false (res < 0))
284 if (errno == EAGAIN) 508 if (errno == EINVAL)
285 { 509 {
286 /* This happens when the ring buffer is full, at least. I assume this means 510 /* This happens for unsupported fds, officially, but in my testing,
287 * that the event was queued synchronously during io_submit, and thus 511 * also randomly happens for supported fds. We fall back to good old
288 * the buffer overflowd. 512 * poll() here, under the assumption that this is a very rare case.
289 * In this case, we just try next loop iteration. 513 * See https://lore.kernel.org/patchwork/patch/1047453/ to see
290 * This should not result in a few fds taking priority, as the interface 514 * discussion about such a case (ttys) where polling for POLLIN
291 * is one-shot, and we submit iocb's in a round-robin fashion. 515 * fails but POLLIN|POLLOUT works.
292 */ 516 */
293 memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits)); 517 struct iocb *iocb = linuxaio_submits [submitted];
518 epoll_modify (EV_A_ iocb->aio_fildes, 0, anfds [iocb->aio_fildes].events);
519 iocb->aio_reqprio = -1; /* mark iocb as epoll */
520
521 res = 1; /* skip this iocb - another iocb, another chance */
522 }
523 else if (errno == EAGAIN)
524 {
525 /* This happens when the ring buffer is full, or some other shit we
526 * don't know and isn't documented. Most likely because we have too
527 * many requests and linux aio can't be assed to handle them.
528 * In this case, we try to allocate a larger ring buffer, freeing
529 * ours first. This might fail, in which case we have to fall back to 100%
530 * epoll.
531 * God, how I hate linux not getting its act together. Ever.
532 */
533 evsys_io_destroy (linuxaio_ctx);
294 linuxaio_submitcnt -= submitted; 534 linuxaio_submitcnt = 0;
535
536 /* rearm all fds with active iocbs */
537 {
538 int fd;
539 for (fd = 0; fd < linuxaio_iocbpmax; ++fd)
540 if (linuxaio_iocbps [fd]->io.aio_buf)
541 linuxaio_fd_rearm (EV_A_ fd);
542 }
543
544 ++linuxaio_iteration;
545 if (linuxaio_io_setup (EV_A) < 0)
546 {
547 /* to bad, we can't get a new aio context, go 100% epoll */
548 linuxaio_free_iocbp (EV_A);
549 ev_io_stop (EV_A_ &linuxaio_epoll_w);
550 ev_ref (EV_A);
551 linuxaio_ctx = 0;
552 backend_modify = epoll_modify;
553 backend_poll = epoll_poll;
554 }
555
295 timeout = 0; 556 timeout = 0;
557 /* it's easiest to handle this mess in another iteration */
296 break; 558 return;
297 } 559 }
560 else if (errno == EBADF)
561 {
562 assert (("libev: event loop rejected bad fd", errno != EBADF));
563 fd_kill (EV_A_ linuxaio_submits [submitted]->aio_fildes);
564
565 res = 1; /* skip this iocb */
566 }
567 else if (errno == EINTR) /* not seen in reality, not documented */
568 res = 0; /* silently ignore and retry */
298 else 569 else
299 ev_syserr ("(libev) linuxaio io_submit"); 570 ev_syserr ("(libev) linuxaio io_submit");
300 571
301 submitted += res; 572 submitted += res;
302 } 573 }
… …
312int 583int
313linuxaio_init (EV_P_ int flags) 584linuxaio_init (EV_P_ int flags)
314{ 585{
315 /* would be great to have a nice test for IOCB_CMD_POLL instead */ 586 /* 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 */ 587 /* 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 */ 588 /* 4.18 introduced IOCB_CMD_POLL, 4.19 made epoll work, and we need that */
589 if (ev_linux_version () < 0x041300)
318 return 0; 590 return 0;
319 591
320 linuxaio_ctx = 0; 592 if (!epoll_init (EV_A_ 0))
321 if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
322 return 0; 593 return 0;
594
595 linuxaio_iteration = 0;
596
597 if (linuxaio_io_setup (EV_A) < 0)
598 {
599 epoll_destroy (EV_A);
600 return 0;
601 }
602
603 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
604 ev_set_priority (&linuxaio_epoll_w, EV_MAXPRI);
605 ev_io_start (EV_A_ &linuxaio_epoll_w);
606 ev_unref (EV_A); /* watcher should not keep loop alive */
323 607
324 backend_modify = linuxaio_modify; 608 backend_modify = linuxaio_modify;
325 backend_poll = linuxaio_poll; 609 backend_poll = linuxaio_poll;
326 610
327 linuxaio_iocbpmax = 0; 611 linuxaio_iocbpmax = 0;
… …
336 620
337inline_size 621inline_size
338void 622void
339linuxaio_destroy (EV_P) 623linuxaio_destroy (EV_P)
340{ 624{
625 epoll_destroy (EV_A);
341 linuxaio_free_iocbp (EV_A); 626 linuxaio_free_iocbp (EV_A);
342 ev_io_destroy (linuxaio_ctx); 627 evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */
343} 628}
344 629
345inline_size 630inline_size
346void 631void
347linuxaio_fork (EV_P) 632linuxaio_fork (EV_P)
348{ 633{
349 /* this frees all iocbs, which is very heavy-handed */ 634 /* this frees all iocbs, which is very heavy-handed */
350 linuxaio_destroy (EV_A); 635 linuxaio_destroy (EV_A);
351 linuxaio_submitcnt = 0; /* all pointers were invalidated */ 636 linuxaio_submitcnt = 0; /* all pointers were invalidated */
352 637
353 linuxaio_ctx = 0; 638 linuxaio_iteration = 0; /* we start over in the child */
354 while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0) 639
640 while (linuxaio_io_setup (EV_A) < 0)
355 ev_syserr ("(libev) linuxaio io_setup"); 641 ev_syserr ("(libev) linuxaio io_setup");
356 642
643 /* forking epoll should also effectively unregister all fds from the backend */
644 epoll_fork (EV_A);
645
646 ev_io_stop (EV_A_ &linuxaio_epoll_w);
647 ev_io_set (EV_A_ &linuxaio_epoll_w, backend_fd, EV_READ);
648 ev_io_start (EV_A_ &linuxaio_epoll_w);
649
650 /* epoll_fork already did this. hopefully */
357 fd_rearm_all (EV_A); 651 /*fd_rearm_all (EV_A);*/
358} 652}
359 653

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