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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 1.39 by root, Mon Jul 1 20:34:31 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 EV_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 */
71 unsigned nr; /* number of io_events */ 109 unsigned nr; /* number of io_events */
72 unsigned head; /* Written to by userland or by kernel. */ 110 unsigned head; /* Written to by userland or by kernel. */
… …
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 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) == 09)
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 }
170 315
171 if (nev) 316 if (nev)
172 { 317 {
173 iocb->io.aio_data = fd;
174 iocb->io.aio_fildes = fd;
175 iocb->io.aio_buf = 318 iocb->io.aio_buf =
176 (nev & EV_READ ? POLLIN : 0) 319 (nev & EV_READ ? POLLIN : 0)
177 | (nev & EV_WRITE ? POLLOUT : 0); 320 | (nev & EV_WRITE ? POLLOUT : 0);
178 321
179 /* queue iocb up for io_submit */ 322 /* queue iocb up for io_submit */
180 /* 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 */
… …
183 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io; 326 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
184 } 327 }
185} 328}
186 329
187static 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
188linuxaio_parse_events (EV_P_ struct io_event *ev, int nr) 346linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
189{ 347{
190 while (nr) 348 while (nr)
191 { 349 {
192 int fd = ev->data; 350 int fd = ev->data;
193 int res = ev->res; 351 int res = ev->res;
194 352
195 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));
196 354
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 */ 355 /* 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 ( 356 fd_event (
207 EV_A_ 357 EV_A_
208 fd, 358 fd,
209 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) 359 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
210 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) 360 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
211 ); 361 );
362
363 /* linux aio is oneshot: rearm fd. TODO: this does more work than strictly needed */
364 linuxaio_fd_rearm (EV_A_ fd);
212 365
213 --nr; 366 --nr;
214 ++ev; 367 ++ev;
215 } 368 }
216} 369}
217 370
218/* get any events from ringbuffer, return true if any were handled */ 371/* get any events from ring buffer, return true if any were handled */
219static int 372static int
220linuxaio_get_events_from_ring (EV_P) 373linuxaio_get_events_from_ring (EV_P)
221{ 374{
222 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; 375 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
223 376
… …
228 unsigned tail = *(volatile unsigned *)&ring->tail; 381 unsigned tail = *(volatile unsigned *)&ring->tail;
229 382
230 if (head == tail) 383 if (head == tail)
231 return 0; 384 return 0;
232 385
233 /* bail out if the ring buffer doesn't match the expected layout */
234 if (ecb_expect_false (ring->magic != AIO_RING_MAGIC)
235 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
236 || ring->header_length != sizeof (struct aio_ring)) /* TODO: or use it to find io_event[0]? */
237 return 0;
238
239 /* make sure the events up to tail are visible */ 386 /* make sure the events up to tail are visible */
240 ECB_MEMORY_FENCE_ACQUIRE; 387 ECB_MEMORY_FENCE_ACQUIRE;
241 388
242 /* parse all available events, but only once, to avoid starvation */ 389 /* parse all available events, but only once, to avoid starvation */
243 if (tail > head) /* normal case around */ 390 if (tail > head) /* normal case around */
… …
246 { 393 {
247 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);
248 linuxaio_parse_events (EV_A_ ring->io_events, tail); 395 linuxaio_parse_events (EV_A_ ring->io_events, tail);
249 } 396 }
250 397
398 ECB_MEMORY_FENCE_RELEASE;
251 /* as an extension to C, we hope that the volatile will makethis atomic and once-only */ 399 /* as an extension to C, we hope that the volatile will make this atomic and once-only */
252 *(volatile unsigned *)&ring->head = tail; 400 *(volatile unsigned *)&ring->head = tail;
253 /* make sure kernel can see our new head value - probably not required */
254 ECB_MEMORY_FENCE_RELEASE;
255 401
256 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]? */
257} 414}
258 415
259/* read at least one event from kernel, or timeout */ 416/* read at least one event from kernel, or timeout */
260inline_size 417inline_size
261void 418void
262linuxaio_get_events (EV_P_ ev_tstamp timeout) 419linuxaio_get_events (EV_P_ ev_tstamp timeout)
263{ 420{
264 struct timespec ts; 421 struct timespec ts;
265 struct io_event ioev; 422 struct io_event ioev[8]; /* 256 octet stack space */
266 int res; 423 int want = 1; /* how many events to request */
424 int ringbuf_valid = linuxaio_ringbuf_valid (EV_A);
267 425
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 */
268 if (linuxaio_get_events_from_ring (EV_A)) 429 if (linuxaio_get_events_from_ring (EV_A))
269 return; 430 return;
270 431
271 /* 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 */
272 /* this degrades to one event per loop iteration */ 433 if (!timeout)
273 /* 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]);
274 439
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
275 ts.tv_sec = (long)timeout; 449 ts.tv_sec = (long)timeout;
276 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9); 450 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
277 451
278 res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts); 452 res = evsys_io_getevents (linuxaio_ctx, 1, want, ioev, &ts);
279 453
454 EV_ACQUIRE_CB;
455
280 if (res < 0) 456 if (res < 0)
281 if (errno == EINTR) 457 if (errno == EINTR)
282 /* ignored */; 458 /* ignored, retry */;
283 else 459 else
284 ev_syserr ("(libev) linuxaio io_getevents"); 460 ev_syserr ("(libev) linuxaio io_getevents");
285 else if (res) 461 else if (res)
286 { 462 {
287 /* at least one event received, handle it and any remaining ones in the ring buffer */ 463 /* at least one event available, handle them */
288 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 */
289 linuxaio_get_events_from_ring (EV_A); 469 linuxaio_get_events_from_ring (EV_A);
290 }
291}
292 470
293#if EPOLL_FALLBACK 471 /* at this point, we should have handled all outstanding events */
294static void 472 break;
295linuxaio_rearm_epoll (EV_P_ struct iocb *iocb, int op) 473 }
296{ 474 else if (res < want)
297 struct epoll_event eev; 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 */
298 480
299 eev.events = EPOLLONESHOT; 481 timeout = 0; /* only wait in the first iteration */
300 if (iocb->aio_buf & POLLIN ) eev.events |= EPOLLIN ; 482 }
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} 483}
307#endif 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);
491}
308 492
309static void 493static void
310linuxaio_poll (EV_P_ ev_tstamp timeout) 494linuxaio_poll (EV_P_ ev_tstamp timeout)
311{ 495{
312 int submitted; 496 int submitted;
313 497
314 /* first phase: submit new iocbs */ 498 /* first phase: submit new iocbs */
315 499
316 /* io_submit might return less than the requested number of iocbs */ 500 /* 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, */ 501 /* 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 */ 502 /* which allows us to pinpoint the erroneous iocb */
319 for (submitted = 0; submitted < linuxaio_submitcnt; ) 503 for (submitted = 0; submitted < linuxaio_submitcnt; )
320 { 504 {
321 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);
322 506
323 if (ecb_expect_false (res < 0)) 507 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) 508 if (errno == EINVAL)
340 { 509 {
341 /* This happens for unsupported fds, officially, but in my testing, 510 /* This happens for unsupported fds, officially, but in my testing,
342 * also randomly happens for supported fds. We fall back to good old 511 * 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. 512 * poll() here, under the assumption that this is a very rare case.
344 * See https://lore.kernel.org/patchwork/patch/1047453/ for evidence 513 * See https://lore.kernel.org/patchwork/patch/1047453/ to see
345 * that the problem is known, but ignored. 514 * discussion about such a case (ttys) where polling for POLLIN
515 * fails but POLLIN|POLLOUT works.
346 */ 516 */
347 struct iocb *iocb = linuxaio_submits [submitted]; 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);
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
556 timeout = 0;
557 /* it's easiest to handle this mess in another iteration */
558 return;
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
348 res = 1; /* skip this iocb */ 565 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 } 566 }
353#endif 567 else if (errno == EINTR) /* not seen in reality, not documented */
568 res = 0; /* silently ignore and retry */
354 else 569 else
355 ev_syserr ("(libev) linuxaio io_submit"); 570 ev_syserr ("(libev) linuxaio io_submit");
356 571
357 submitted += res; 572 submitted += res;
358 } 573 }
… …
362 /* second phase: fetch and parse events */ 577 /* second phase: fetch and parse events */
363 578
364 linuxaio_get_events (EV_A_ timeout); 579 linuxaio_get_events (EV_A_ timeout);
365} 580}
366 581
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 582inline_size
406int 583int
407linuxaio_init (EV_P_ int flags) 584linuxaio_init (EV_P_ int flags)
408{ 585{
409 /* 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 */
410 /* 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 */
411#if EPOLL_FALLBACK 588 /* 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) 589 if (ev_linux_version () < 0x041300)
414 return 0; 590 return 0;
415#else 591
416 /* 4.18 introduced IOCB_CMD_POLL */ 592 if (!epoll_init (EV_A_ 0))
417 if (ev_linux_version () < 0x041200)
418 return 0; 593 return 0;
419#endif
420 594
421 linuxaio_ctx = 0; 595 linuxaio_iteration = 0;
422 if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
423 return 0;
424 596
425#if EPOLL_FALLBACK 597 if (linuxaio_io_setup (EV_A) < 0)
426 backend_fd = ev_epoll_create ();
427 if (backend_fd < 0)
428 { 598 {
429 ev_io_destroy (linuxaio_ctx); 599 epoll_destroy (EV_A);
430 return 0; 600 return 0;
431 } 601 }
432 602
433 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ); 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);
434 ev_io_start (EV_A_ &linuxaio_epoll_w); 605 ev_io_start (EV_A_ &linuxaio_epoll_w);
435 ev_unref (EV_A); /* watcher should not keep loop alive */ 606 ev_unref (EV_A); /* watcher should not keep loop alive */
436#endif
437 607
438 backend_modify = linuxaio_modify; 608 backend_modify = linuxaio_modify;
439 backend_poll = linuxaio_poll; 609 backend_poll = linuxaio_poll;
440 610
441 linuxaio_iocbpmax = 0; 611 linuxaio_iocbpmax = 0;
… …
450 620
451inline_size 621inline_size
452void 622void
453linuxaio_destroy (EV_P) 623linuxaio_destroy (EV_P)
454{ 624{
455#if EPOLL_FALLBACK 625 epoll_destroy (EV_A);
456 close (backend_fd);
457#endif
458 linuxaio_free_iocbp (EV_A); 626 linuxaio_free_iocbp (EV_A);
459 ev_io_destroy (linuxaio_ctx); 627 evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */
460} 628}
461 629
462inline_size 630inline_size
463void 631void
464linuxaio_fork (EV_P) 632linuxaio_fork (EV_P)
465{ 633{
466 /* this frees all iocbs, which is very heavy-handed */ 634 /* this frees all iocbs, which is very heavy-handed */
467 linuxaio_destroy (EV_A); 635 linuxaio_destroy (EV_A);
468 linuxaio_submitcnt = 0; /* all pointers were invalidated */ 636 linuxaio_submitcnt = 0; /* all pointers were invalidated */
469 637
470 linuxaio_ctx = 0; 638 linuxaio_iteration = 0; /* we start over in the child */
471 while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0) 639
640 while (linuxaio_io_setup (EV_A) < 0)
472 ev_syserr ("(libev) linuxaio io_setup"); 641 ev_syserr ("(libev) linuxaio io_setup");
473 642
474#if EPOLL_FALLBACK 643 /* forking epoll should also effectively unregister all fds from the backend */
475 while ((backend_fd = ev_epoll_create ()) < 0) 644 epoll_fork (EV_A);
476 ev_syserr ("(libev) linuxaio epoll_create");
477 645
478 ev_io_stop (EV_A_ &linuxaio_epoll_w); 646 ev_io_stop (EV_A_ &linuxaio_epoll_w);
479 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ); 647 ev_io_set (EV_A_ &linuxaio_epoll_w, backend_fd, EV_READ);
480 ev_io_start (EV_A_ &linuxaio_epoll_w); 648 ev_io_start (EV_A_ &linuxaio_epoll_w);
481#endif
482 649
650 /* epoll_fork already did this. hopefully */
483 fd_rearm_all (EV_A); 651 /*fd_rearm_all (EV_A);*/
484} 652}
485 653

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