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Comparing libev/ev_linuxaio.c (file contents):
Revision 1.5 by root, Fri Jun 21 03:41:40 2019 UTC vs.
Revision 1.42 by root, Mon Jul 1 20:47:38 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 4kn 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 * so the calculation below will use "exactly" 8kB for the ring buffer
48 */
49#define EV_LINUXAIO_DEPTH (256 / 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
77static int 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
172inline_size
173int
78ev_io_setup (unsigned nr_events, aio_context_t *ctx_idp) 174evsys_io_setup (unsigned nr_events, aio_context_t *ctx_idp)
79{ 175{
80 return syscall (SYS_io_setup, nr_events, ctx_idp); 176 return ev_syscall2 (SYS_io_setup, nr_events, ctx_idp);
81} 177}
82 178
83static int 179inline_size
180int
84ev_io_destroy (aio_context_t ctx_id) 181evsys_io_destroy (aio_context_t ctx_id)
85{ 182{
86 return syscall (SYS_io_destroy, ctx_id); 183 return ev_syscall1 (SYS_io_destroy, ctx_id);
87} 184}
88 185
89static int 186inline_size
187int
90ev_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[])
91{ 189{
92 return syscall (SYS_io_submit, ctx_id, nr, cbp); 190 return ev_syscall3 (SYS_io_submit, ctx_id, nr, cbp);
93} 191}
94 192
95static int 193inline_size
194int
96ev_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)
97{ 196{
98 return syscall (SYS_io_cancel, ctx_id, cbp, result); 197 return ev_syscall3 (SYS_io_cancel, ctx_id, cbp, result);
99} 198}
100 199
101static int 200inline_size
201int
102ev_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)
103{ 203{
104 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);
105} 205}
106
107typedef void (*ev_io_cb) (long nr, struct io_event *events);
108 206
109/*****************************************************************************/ 207/*****************************************************************************/
110/* actual backed implementation */ 208/* actual backed implementation */
111 209
112/* two iocbs for every fd, one for read, one for write */ 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
246/* we use out own wrapper structure in case we ever want to do something "clever" */
113typedef struct aniocb 247typedef struct aniocb
114{ 248{
115 struct iocb io; 249 struct iocb io;
116 /*int inuse;*/ 250 /*int inuse;*/
117} *ANIOCBP; 251} *ANIOCBP;
118 252
119inline_size 253inline_size
120void 254void
121linuxaio_array_needsize_iocbp (ANIOCBP *base, int count) 255linuxaio_array_needsize_iocbp (ANIOCBP *base, int offset, int count)
122{ 256{
123 /* TODO: quite the overhead to allocate every iocb separately */
124 while (count--) 257 while (count--)
125 { 258 {
259 /* TODO: quite the overhead to allocate every iocb separately, maybe use our own allocator? */
126 *base = (ANIOCBP)ev_malloc (sizeof (**base)); 260 ANIOCBP iocb = (ANIOCBP)ev_malloc (sizeof (*iocb));
127 /* 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 */
128 memset (*base, 0, sizeof (**base)); 265 memset (iocb, 0, sizeof (*iocb));
129 /* would be nice to initialize fd/data as well */ 266
130 (*base)->io.aio_lio_opcode = IOCB_CMD_POLL; 267 iocb->io.aio_lio_opcode = IOCB_CMD_POLL;
131 ++base; 268 iocb->io.aio_data = offset;
132 } 269 iocb->io.aio_fildes = offset;
133}
134 270
271 base [offset++] = iocb;
272 }
273}
274
275ecb_cold
135static void 276static void
136linuxaio_free_iocbp (EV_P) 277linuxaio_free_iocbp (EV_P)
137{ 278{
138 while (linuxaio_iocbpmax--) 279 while (linuxaio_iocbpmax--)
139 ev_free (linuxaio_iocbps [linuxaio_iocbpmax]); 280 ev_free (linuxaio_iocbps [linuxaio_iocbpmax]);
140 281
141 /* next resize will completely reallocate the array */ 282 linuxaio_iocbpmax = 0; /* next resize will completely reallocate the array, at some overhead */
142 linuxaio_iocbpmax = 0;
143 linuxaio_submitcnt = 0; /* all pointers invalidated */
144} 283}
145 284
146static void 285static void
147linuxaio_modify (EV_P_ int fd, int oev, int nev) 286linuxaio_modify (EV_P_ int fd, int oev, int nev)
148{ 287{
149 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);
150 struct aniocb *iocb = linuxaio_iocbps [fd]; 289 ANIOCBP iocb = linuxaio_iocbps [fd];
151 290
291 if (ecb_expect_false (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 }
299
300 if (ecb_expect_false (iocb->io.aio_buf))
301 {
302 /* iocb active, so cancel it first before resubmit */
303 for (;;)
304 {
305 /* on all relevant kernels, io_cancel fails with EINPROGRESS on "success" */
306 if (ecb_expect_false (evsys_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0) == 0))
307 break;
308
309 if (ecb_expect_true (errno == EINPROGRESS))
310 break;
311
312 /* the EINPROGRESS test is for nicer error message. clumsy. */
313 assert (("libev: linuxaio unexpected io_cancel failed", errno != EINPROGRESS && errno != EINTR));
314 }
315 }
316
152 if (iocb->io.aio_buf) 317 iocb->io.aio_buf =
153 ev_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0); /* always returns an error relevant kernels */ 318 (nev & EV_READ ? POLLIN : 0)
319 | (nev & EV_WRITE ? POLLOUT : 0);
154 320
155 if (nev) 321 if (nev)
156 { 322 {
157 iocb->io.aio_data = fd;
158 iocb->io.aio_fildes = fd;
159 iocb->io.aio_buf =
160 (nev & EV_READ ? POLLIN : 0)
161 | (nev & EV_WRITE ? POLLOUT : 0);
162
163 /* queue iocb up for io_submit */ 323 /* queue iocb up for io_submit */
164 /* this assumes we only ever get one call per fd per loop iteration */ 324 /* this assumes we only ever get one call per fd per loop iteration */
165 ++linuxaio_submitcnt; 325 ++linuxaio_submitcnt;
166 array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit); 326 array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit);
167 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io; 327 linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io;
168 } 328 }
169} 329}
170 330
171static void 331static void
332linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents)
333{
334 epoll_poll (EV_A_ 0);
335}
336
337inline_speed
338void
339linuxaio_fd_rearm (EV_P_ int fd)
340{
341 anfds [fd].events = 0;
342 linuxaio_iocbps [fd]->io.aio_buf = 0;
343 fd_change (EV_A_ fd, EV_ANFD_REIFY);
344}
345
346static void
172linuxaio_parse_events (EV_P_ struct io_event *ev, int nr) 347linuxaio_parse_events (EV_P_ struct io_event *ev, int nr)
173{ 348{
174 while (nr) 349 while (nr)
175 { 350 {
176 int fd = ev->data; 351 int fd = ev->data;
177 int res = ev->res; 352 int res = ev->res;
178 353
179 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax)); 354 assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax));
180 355
181 /* linux aio is oneshot: rearm fd */
182 linuxaio_iocbps [fd]->io.aio_buf = 0;
183 anfds [fd].events = 0;
184 fd_change (EV_A_ fd, 0);
185
186 /* feed events, we do not expect or handle POLLNVAL */ 356 /* feed events, we do not expect or handle POLLNVAL */
187 if (ecb_expect_false (res & POLLNVAL))
188 fd_kill (EV_A_ fd);
189 else
190 fd_event ( 357 fd_event (
191 EV_A_ 358 EV_A_
192 fd, 359 fd,
193 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) 360 (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0)
194 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) 361 | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0)
195 ); 362 );
363
364 /* linux aio is oneshot: rearm fd. TODO: this does more work than strictly needed */
365 linuxaio_fd_rearm (EV_A_ fd);
196 366
197 --nr; 367 --nr;
198 ++ev; 368 ++ev;
199 } 369 }
200} 370}
201 371
202/* get any events from ringbuffer, return true if any were handled */ 372/* get any events from ring buffer, return true if any were handled */
203static int 373static int
204linuxaio_get_events_from_ring (EV_P) 374linuxaio_get_events_from_ring (EV_P)
205{ 375{
206 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; 376 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
207 377
378 /* the kernel reads and writes both of these variables, */
379 /* as a C extension, we assume that volatile use here */
380 /* both makes reads atomic and once-only */
381 unsigned head = *(volatile unsigned *)&ring->head;
382 unsigned tail = *(volatile unsigned *)&ring->tail;
383
384 if (head == tail)
385 return 0;
386
387 /* make sure the events up to tail are visible */
208 ECB_MEMORY_FENCE_ACQUIRE; 388 ECB_MEMORY_FENCE_ACQUIRE;
209
210 unsigned head = ring->head;
211 unsigned tail = *(volatile unsigned *)&ring->tail;
212
213 if (ring->magic != AIO_RING_MAGIC
214 || ring->incompat_features != AIO_RING_INCOMPAT_FEATURES
215 || ring->header_length != sizeof (struct aio_ring) /* TODO: or use it to find io_event[0]? */
216 || head == tail)
217 return 0;
218 389
219 /* parse all available events, but only once, to avoid starvation */ 390 /* parse all available events, but only once, to avoid starvation */
220 if (tail > head) /* normal case around */ 391 if (tail > head) /* normal case around */
221 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head); 392 linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head);
222 else
223 {
224 /* wrapped around */ 393 else /* wrapped around */
394 {
225 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head); 395 linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
226 linuxaio_parse_events (EV_A_ ring->io_events, tail); 396 linuxaio_parse_events (EV_A_ ring->io_events, tail);
227 } 397 }
228 398
229 ring->head = tail; 399 ECB_MEMORY_FENCE_RELEASE;
400 /* as an extension to C, we hope that the volatile will make this atomic and once-only */
401 *(volatile unsigned *)&ring->head = tail;
230 402
231 return 1; 403 return 1;
404}
405
406inline_size
407int
408linuxaio_ringbuf_valid (EV_P)
409{
410 struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
411
412 return ecb_expect_true (ring->magic == AIO_RING_MAGIC)
413 && ring->incompat_features == EV_AIO_RING_INCOMPAT_FEATURES
414 && ring->header_length == sizeof (struct aio_ring); /* TODO: or use it to find io_event[0]? */
232} 415}
233 416
234/* read at least one event from kernel, or timeout */ 417/* read at least one event from kernel, or timeout */
235inline_size 418inline_size
236void 419void
237linuxaio_get_events (EV_P_ ev_tstamp timeout) 420linuxaio_get_events (EV_P_ ev_tstamp timeout)
238{ 421{
239 struct timespec ts; 422 struct timespec ts;
240 struct io_event ioev; 423 struct io_event ioev[8]; /* 256 octet stack space */
241 int res; 424 int want = 1; /* how many events to request */
425 int ringbuf_valid = linuxaio_ringbuf_valid (EV_A);
242 426
427 if (ecb_expect_true (ringbuf_valid))
428 {
429 /* if the ring buffer has any events, we don't wait or call the kernel at all */
243 if (linuxaio_get_events_from_ring (EV_A)) 430 if (linuxaio_get_events_from_ring (EV_A))
244 return; 431 return;
245 432
246 /* no events, so wait for at least one, then poll ring buffer again */ 433 /* if the ring buffer is empty, and we don't have a timeout, then don't call the kernel */
247 /* this degraded to one event per loop iteration */ 434 if (!timeout)
248 /* if the ring buffer changes layout, but so be it */ 435 return;
436 }
437 else
438 /* no ringbuffer, request slightly larger batch */
439 want = sizeof (ioev) / sizeof (ioev [0]);
249 440
441 /* no events, so wait for some
442 * for fairness reasons, we do this in a loop, to fetch all events
443 */
444 for (;;)
445 {
446 int res;
447
448 EV_RELEASE_CB;
449
250 ts.tv_sec = (long)timeout; 450 ts.tv_sec = (long)timeout;
251 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9); 451 ts.tv_nsec = (long)((timeout - ts.tv_sec) * 1e9);
252 452
253 res = ev_io_getevents (linuxaio_ctx, 1, 1, &ioev, &ts); 453 res = evsys_io_getevents (linuxaio_ctx, 1, want, ioev, &ts);
254 454
455 EV_ACQUIRE_CB;
456
255 if (res < 0) 457 if (res < 0)
458 if (errno == EINTR)
459 /* ignored, retry */;
460 else
256 ev_syserr ("(libev) io_getevents"); 461 ev_syserr ("(libev) linuxaio io_getevents");
257 else if (res) 462 else if (res)
258 { 463 {
259 /* at least one event received, handle it and any remaining ones in the ring buffer */ 464 /* at least one event available, handle them */
260 linuxaio_parse_events (EV_A_ &ioev, 1); 465 linuxaio_parse_events (EV_A_ ioev, res);
466
467 if (ecb_expect_true (ringbuf_valid))
468 {
469 /* if we have a ring buffer, handle any remaining events in it */
261 linuxaio_get_events_from_ring (EV_A); 470 linuxaio_get_events_from_ring (EV_A);
471
472 /* at this point, we should have handled all outstanding events */
473 break;
474 }
475 else if (res < want)
476 /* otherwise, if there were fewere events than we wanted, we assume there are no more */
477 break;
478 }
479 else
480 break; /* no events from the kernel, we are done */
481
482 timeout = 0; /* only wait in the first iteration */
262 } 483 }
484}
485
486inline_size
487int
488linuxaio_io_setup (EV_P)
489{
490 linuxaio_ctx = 0;
491 return evsys_io_setup (linuxaio_nr_events (EV_A), &linuxaio_ctx);
263} 492}
264 493
265static void 494static void
266linuxaio_poll (EV_P_ ev_tstamp timeout) 495linuxaio_poll (EV_P_ ev_tstamp timeout)
267{ 496{
… …
269 498
270 /* first phase: submit new iocbs */ 499 /* first phase: submit new iocbs */
271 500
272 /* io_submit might return less than the requested number of iocbs */ 501 /* io_submit might return less than the requested number of iocbs */
273 /* this is, afaics, only because of errors, but we go by the book and use a loop, */ 502 /* this is, afaics, only because of errors, but we go by the book and use a loop, */
274 /* which allows us to pinpoint the errornous iocb */ 503 /* which allows us to pinpoint the erroneous iocb */
275 for (submitted = 0; submitted < linuxaio_submitcnt; ) 504 for (submitted = 0; submitted < linuxaio_submitcnt; )
276 { 505 {
277 int res = ev_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted); 506 int res = evsys_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted);
278 507
279 if (res < 0) 508 if (ecb_expect_false (res < 0))
280 if (errno == EAGAIN) 509 if (errno == EINVAL)
281 { 510 {
282 /* This happens when the ring buffer is full, at least. I assume this means 511 /* This happens for unsupported fds, officially, but in my testing,
283 * that the event was queued synchronously during io_submit, and thus 512 * also randomly happens for supported fds. We fall back to good old
284 * the buffer overflowd. 513 * poll() here, under the assumption that this is a very rare case.
285 * In this case, we just try next loop iteration. 514 * See https://lore.kernel.org/patchwork/patch/1047453/ to see
515 * discussion about such a case (ttys) where polling for POLLIN
516 * fails but POLLIN|POLLOUT works.
286 */ 517 */
287 memmove (linuxaio_submits, linuxaio_submits + submitted, (linuxaio_submitcnt - submitted) * sizeof (*linuxaio_submits)); 518 struct iocb *iocb = linuxaio_submits [submitted];
519 epoll_modify (EV_A_ iocb->aio_fildes, 0, anfds [iocb->aio_fildes].events);
520 iocb->aio_reqprio = -1; /* mark iocb as epoll */
521
522 res = 1; /* skip this iocb - another iocb, another chance */
523 }
524 else if (errno == EAGAIN)
525 {
526 /* This happens when the ring buffer is full, or some other shit we
527 * don't know and isn't documented. Most likely because we have too
528 * many requests and linux aio can't be assed to handle them.
529 * In this case, we try to allocate a larger ring buffer, freeing
530 * ours first. This might fail, in which case we have to fall back to 100%
531 * epoll.
532 * God, how I hate linux not getting its act together. Ever.
533 */
534 evsys_io_destroy (linuxaio_ctx);
288 linuxaio_submitcnt -= submitted; 535 linuxaio_submitcnt = 0;
536
537 /* rearm all fds with active iocbs */
538 {
539 int fd;
540 for (fd = 0; fd < linuxaio_iocbpmax; ++fd)
541 if (linuxaio_iocbps [fd]->io.aio_buf)
542 linuxaio_fd_rearm (EV_A_ fd);
543 }
544
545 ++linuxaio_iteration;
546 if (linuxaio_io_setup (EV_A) < 0)
547 {
548 /* to bad, we can't get a new aio context, go 100% epoll */
549 linuxaio_free_iocbp (EV_A);
550 ev_io_stop (EV_A_ &linuxaio_epoll_w);
551 ev_ref (EV_A);
552 linuxaio_ctx = 0;
553 backend_modify = epoll_modify;
554 backend_poll = epoll_poll;
555 }
556
289 timeout = 0; 557 timeout = 0;
558 /* it's easiest to handle this mess in another iteration */
290 break; 559 return;
291 } 560 }
561 else if (errno == EBADF)
562 {
563 assert (("libev: event loop rejected bad fd", errno != EBADF));
564 fd_kill (EV_A_ linuxaio_submits [submitted]->aio_fildes);
565
566 res = 1; /* skip this iocb */
567 }
568 else if (errno == EINTR) /* not seen in reality, not documented */
569 res = 0; /* silently ignore and retry */
292 else 570 else
293 /* TODO: we get EAGAIN when the ring buffer is full for some reason */
294 /* TODO: should we always just try next time? */
295 ev_syserr ("(libev) io_submit"); 571 ev_syserr ("(libev) linuxaio io_submit");
296 572
297 submitted += res; 573 submitted += res;
298 } 574 }
299 575
300 linuxaio_submitcnt = 0; 576 linuxaio_submitcnt = 0;
… …
308int 584int
309linuxaio_init (EV_P_ int flags) 585linuxaio_init (EV_P_ int flags)
310{ 586{
311 /* would be great to have a nice test for IOCB_CMD_POLL instead */ 587 /* would be great to have a nice test for IOCB_CMD_POLL instead */
312 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */ 588 /* also: test some semi-common fd types, such as files and ttys in recommended_backends */
313 if (ev_linux_version () < 0x041200) /* 4.18 introduced IOCB_CMD_POLL */ 589 /* 4.18 introduced IOCB_CMD_POLL, 4.19 made epoll work, and we need that */
590 if (ev_linux_version () < 0x041300)
314 return 0; 591 return 0;
315 592
316 linuxaio_ctx = 0; 593 if (!epoll_init (EV_A_ 0))
317 if (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0)
318 return 0; 594 return 0;
595
596 linuxaio_iteration = 0;
597
598 if (linuxaio_io_setup (EV_A) < 0)
599 {
600 epoll_destroy (EV_A);
601 return 0;
602 }
603
604 ev_io_init (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
605 ev_set_priority (&linuxaio_epoll_w, EV_MAXPRI);
606 ev_io_start (EV_A_ &linuxaio_epoll_w);
607 ev_unref (EV_A); /* watcher should not keep loop alive */
319 608
320 backend_modify = linuxaio_modify; 609 backend_modify = linuxaio_modify;
321 backend_poll = linuxaio_poll; 610 backend_poll = linuxaio_poll;
322 611
323 linuxaio_iocbpmax = 0; 612 linuxaio_iocbpmax = 0;
… …
332 621
333inline_size 622inline_size
334void 623void
335linuxaio_destroy (EV_P) 624linuxaio_destroy (EV_P)
336{ 625{
626 epoll_destroy (EV_A);
337 linuxaio_free_iocbp (EV_A); 627 linuxaio_free_iocbp (EV_A);
338 ev_io_destroy (linuxaio_ctx); 628 evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */
339} 629}
340 630
341inline_size 631inline_size
342void 632void
343linuxaio_fork (EV_P) 633linuxaio_fork (EV_P)
344{ 634{
345 /* TODO: verify and test */ 635 /* this frees all iocbs, which is very heavy-handed */
346 linuxaio_destroy (EV_A); 636 linuxaio_destroy (EV_A);
637 linuxaio_submitcnt = 0; /* all pointers were invalidated */
347 638
348 linuxaio_ctx = 0; 639 linuxaio_iteration = 0; /* we start over in the child */
349 while (ev_io_setup (EV_LINUXAIO_DEPTH, &linuxaio_ctx) < 0) 640
641 while (linuxaio_io_setup (EV_A) < 0)
350 ev_syserr ("(libev) io_setup"); 642 ev_syserr ("(libev) linuxaio io_setup");
351 643
644 /* forking epoll should also effectively unregister all fds from the backend */
645 epoll_fork (EV_A);
646
647 ev_io_stop (EV_A_ &linuxaio_epoll_w);
648 ev_io_set (EV_A_ &linuxaio_epoll_w, backend_fd, EV_READ);
649 ev_io_start (EV_A_ &linuxaio_epoll_w);
650
651 /* epoll_fork already did this. hopefully */
352 fd_rearm_all (EV_A); 652 /*fd_rearm_all (EV_A);*/
353} 653}
354 654

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