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Diffstat (limited to 'libev/ev_linuxaio.c')
| -rw-r--r-- | libev/ev_linuxaio.c | 621 |
1 files changed, 621 insertions, 0 deletions
diff --git a/libev/ev_linuxaio.c b/libev/ev_linuxaio.c new file mode 100644 index 0000000..3e17850 --- /dev/null +++ b/libev/ev_linuxaio.c @@ -0,0 +1,621 @@ +/* + * libev linux aio fd activity backend + * + * Copyright (c) 2019 Marc Alexander Lehmann <libev@schmorp.de> + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without modifica- + * tion, are permitted provided that the following conditions are met: + * + * 1. Redistributions of source code must retain the above copyright notice, + * this list of conditions and the following disclaimer. + * + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER- + * CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO + * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE- + * CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, + * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; + * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, + * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH- + * ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED + * OF THE POSSIBILITY OF SUCH DAMAGE. + * + * Alternatively, the contents of this file may be used under the terms of + * the GNU General Public License ("GPL") version 2 or any later version, + * in which case the provisions of the GPL are applicable instead of + * the above. If you wish to allow the use of your version of this file + * only under the terms of the GPL and not to allow others to use your + * version of this file under the BSD license, indicate your decision + * by deleting the provisions above and replace them with the notice + * and other provisions required by the GPL. If you do not delete the + * provisions above, a recipient may use your version of this file under + * either the BSD or the GPL. + */ + +/* + * general notes about linux aio: + * + * a) at first, the linux aio IOCB_CMD_POLL functionality introduced in + * 4.18 looks too good to be true: both watchers and events can be + * batched, and events can even be handled in userspace using + * a ring buffer shared with the kernel. watchers can be canceled + * regardless of whether the fd has been closed. no problems with fork. + * ok, the ring buffer is 200% undocumented (there isn't even a + * header file), but otherwise, it's pure bliss! + * b) ok, watchers are one-shot, so you have to re-arm active ones + * on every iteration. so much for syscall-less event handling, + * but at least these re-arms can be batched, no big deal, right? + * c) well, linux as usual: the documentation lies to you: io_submit + * sometimes returns EINVAL because the kernel doesn't feel like + * handling your poll mask - ttys can be polled for POLLOUT, + * POLLOUT|POLLIN, but polling for POLLIN fails. just great, + * so we have to fall back to something else (hello, epoll), + * but at least the fallback can be slow, because these are + * exceptional cases, right? + * d) hmm, you have to tell the kernel the maximum number of watchers + * you want to queue when initialising the aio context. but of + * course the real limit is magically calculated in the kernel, and + * is often higher then we asked for. so we just have to destroy + * the aio context and re-create it a bit larger if we hit the limit. + * (starts to remind you of epoll? well, it's a bit more deterministic + * and less gambling, but still ugly as hell). + * e) that's when you find out you can also hit an arbitrary system-wide + * limit. or the kernel simply doesn't want to handle your watchers. + * what the fuck do we do then? you guessed it, in the middle + * of event handling we have to switch to 100% epoll polling. and + * that better is as fast as normal epoll polling, so you practically + * have to use the normal epoll backend with all its quirks. + * f) end result of this train wreck: it inherits all the disadvantages + * from epoll, while adding a number on its own. why even bother to use + * it? because if conditions are right and your fds are supported and you + * don't hit a limit, this backend is actually faster, doesn't gamble with + * your fds, batches watchers and events and doesn't require costly state + * recreates. well, until it does. + * g) all of this makes this backend use almost twice as much code as epoll. + * which in turn uses twice as much code as poll. and that#s not counting + * the fact that this backend also depends on the epoll backend, making + * it three times as much code as poll, or kqueue. + * h) bleah. why can't linux just do kqueue. sure kqueue is ugly, but by now + * it's clear that whatever linux comes up with is far, far, far worse. + */ + +#include <sys/time.h> /* actually linux/time.h, but we must assume they are compatible */ +#include <poll.h> +#include <linux/aio_abi.h> + +/*****************************************************************************/ +/* syscall wrapdadoop - this section has the raw api/abi definitions */ + +#include <sys/syscall.h> /* no glibc wrappers */ + +/* aio_abi.h is not versioned in any way, so we cannot test for its existance */ +#define IOCB_CMD_POLL 5 + +/* taken from linux/fs/aio.c. yup, that's a .c file. + * not only is this totally undocumented, not even the source code + * can tell you what the future semantics of compat_features and + * incompat_features are, or what header_length actually is for. + */ +#define AIO_RING_MAGIC 0xa10a10a1 +#define EV_AIO_RING_INCOMPAT_FEATURES 0 +struct aio_ring +{ + unsigned id; /* kernel internal index number */ + unsigned nr; /* number of io_events */ + unsigned head; /* Written to by userland or by kernel. */ + unsigned tail; + + unsigned magic; + unsigned compat_features; + unsigned incompat_features; + unsigned header_length; /* size of aio_ring */ + + struct io_event io_events[0]; +}; + +inline_size +int +evsys_io_setup (unsigned nr_events, aio_context_t *ctx_idp) +{ + return ev_syscall2 (SYS_io_setup, nr_events, ctx_idp); +} + +inline_size +int +evsys_io_destroy (aio_context_t ctx_id) +{ + return ev_syscall1 (SYS_io_destroy, ctx_id); +} + +inline_size +int +evsys_io_submit (aio_context_t ctx_id, long nr, struct iocb *cbp[]) +{ + return ev_syscall3 (SYS_io_submit, ctx_id, nr, cbp); +} + +inline_size +int +evsys_io_cancel (aio_context_t ctx_id, struct iocb *cbp, struct io_event *result) +{ + return ev_syscall3 (SYS_io_cancel, ctx_id, cbp, result); +} + +inline_size +int +evsys_io_getevents (aio_context_t ctx_id, long min_nr, long nr, struct io_event *events, struct timespec *timeout) +{ + return ev_syscall5 (SYS_io_getevents, ctx_id, min_nr, nr, events, timeout); +} + +/*****************************************************************************/ +/* actual backed implementation */ + +ecb_cold +static int +linuxaio_nr_events (EV_P) +{ + /* we start with 16 iocbs and incraese from there + * that's tiny, but the kernel has a rather low system-wide + * limit that can be reached quickly, so let's be parsimonious + * with this resource. + * Rest assured, the kernel generously rounds up small and big numbers + * in different ways (but doesn't seem to charge you for it). + * The 15 here is because the kernel usually has a power of two as aio-max-nr, + * and this helps to take advantage of that limit. + */ + + /* we try to fill 4kB pages exactly. + * the ring buffer header is 32 bytes, every io event is 32 bytes. + * the kernel takes the io requests number, doubles it, adds 2 + * and adds the ring buffer. + * the way we use this is by starting low, and then roughly doubling the + * size each time we hit a limit. + */ + + int requests = 15 << linuxaio_iteration; + int one_page = (4096 + / sizeof (struct io_event) ) / 2; /* how many fit into one page */ + int first_page = ((4096 - sizeof (struct aio_ring)) + / sizeof (struct io_event) - 2) / 2; /* how many fit into the first page */ + + /* if everything fits into one page, use count exactly */ + if (requests > first_page) + /* otherwise, round down to full pages and add the first page */ + requests = requests / one_page * one_page + first_page; + + return requests; +} + +/* we use out own wrapper structure in case we ever want to do something "clever" */ +typedef struct aniocb +{ + struct iocb io; + /*int inuse;*/ +} *ANIOCBP; + +inline_size +void +linuxaio_array_needsize_iocbp (ANIOCBP *base, int offset, int count) +{ + while (count--) + { + /* TODO: quite the overhead to allocate every iocb separately, maybe use our own allocator? */ + ANIOCBP iocb = (ANIOCBP)ev_malloc (sizeof (*iocb)); + + /* full zero initialise is probably not required at the moment, but + * this is not well documented, so we better do it. + */ + memset (iocb, 0, sizeof (*iocb)); + + iocb->io.aio_lio_opcode = IOCB_CMD_POLL; + iocb->io.aio_fildes = offset; + + base [offset++] = iocb; + } +} + +ecb_cold +static void +linuxaio_free_iocbp (EV_P) +{ + while (linuxaio_iocbpmax--) + ev_free (linuxaio_iocbps [linuxaio_iocbpmax]); + + linuxaio_iocbpmax = 0; /* next resize will completely reallocate the array, at some overhead */ +} + +static void +linuxaio_modify (EV_P_ int fd, int oev, int nev) +{ + array_needsize (ANIOCBP, linuxaio_iocbps, linuxaio_iocbpmax, fd + 1, linuxaio_array_needsize_iocbp); + ANIOCBP iocb = linuxaio_iocbps [fd]; + ANFD *anfd = &anfds [fd]; + + if (ecb_expect_false (iocb->io.aio_reqprio < 0)) + { + /* we handed this fd over to epoll, so undo this first */ + /* we do it manually because the optimisations on epoll_modify won't do us any good */ + epoll_ctl (backend_fd, EPOLL_CTL_DEL, fd, 0); + anfd->emask = 0; + iocb->io.aio_reqprio = 0; + } + else if (ecb_expect_false (iocb->io.aio_buf)) + { + /* iocb active, so cancel it first before resubmit */ + /* this assumes we only ever get one call per fd per loop iteration */ + for (;;) + { + /* on all relevant kernels, io_cancel fails with EINPROGRESS on "success" */ + if (ecb_expect_false (evsys_io_cancel (linuxaio_ctx, &iocb->io, (struct io_event *)0) == 0)) + break; + + if (ecb_expect_true (errno == EINPROGRESS)) + break; + + /* the EINPROGRESS test is for nicer error message. clumsy. */ + if (errno != EINTR) + { + assert (("libev: linuxaio unexpected io_cancel failed", errno != EINTR && errno != EINPROGRESS)); + break; + } + } + + /* increment generation counter to avoid handling old events */ + ++anfd->egen; + } + + iocb->io.aio_buf = + (nev & EV_READ ? POLLIN : 0) + | (nev & EV_WRITE ? POLLOUT : 0); + + if (nev) + { + iocb->io.aio_data = (uint32_t)fd | ((__u64)(uint32_t)anfd->egen << 32); + + /* queue iocb up for io_submit */ + /* this assumes we only ever get one call per fd per loop iteration */ + ++linuxaio_submitcnt; + array_needsize (struct iocb *, linuxaio_submits, linuxaio_submitmax, linuxaio_submitcnt, array_needsize_noinit); + linuxaio_submits [linuxaio_submitcnt - 1] = &iocb->io; + } +} + +static void +linuxaio_epoll_cb (EV_P_ struct ev_io *w, int revents) +{ + epoll_poll (EV_A_ 0); +} + +inline_speed +void +linuxaio_fd_rearm (EV_P_ int fd) +{ + anfds [fd].events = 0; + linuxaio_iocbps [fd]->io.aio_buf = 0; + fd_change (EV_A_ fd, EV_ANFD_REIFY); +} + +static void +linuxaio_parse_events (EV_P_ struct io_event *ev, int nr) +{ + while (nr) + { + int fd = ev->data & 0xffffffff; + uint32_t gen = ev->data >> 32; + int res = ev->res; + + assert (("libev: iocb fd must be in-bounds", fd >= 0 && fd < anfdmax)); + + /* only accept events if generation counter matches */ + if (ecb_expect_true (gen == (uint32_t)anfds [fd].egen)) + { + /* feed events, we do not expect or handle POLLNVAL */ + fd_event ( + EV_A_ + fd, + (res & (POLLOUT | POLLERR | POLLHUP) ? EV_WRITE : 0) + | (res & (POLLIN | POLLERR | POLLHUP) ? EV_READ : 0) + ); + + /* linux aio is oneshot: rearm fd. TODO: this does more work than strictly needed */ + linuxaio_fd_rearm (EV_A_ fd); + } + + --nr; + ++ev; + } +} + +/* get any events from ring buffer, return true if any were handled */ +static int +linuxaio_get_events_from_ring (EV_P) +{ + struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; + unsigned head, tail; + + /* the kernel reads and writes both of these variables, */ + /* as a C extension, we assume that volatile use here */ + /* both makes reads atomic and once-only */ + head = *(volatile unsigned *)&ring->head; + ECB_MEMORY_FENCE_ACQUIRE; + tail = *(volatile unsigned *)&ring->tail; + + if (head == tail) + return 0; + + /* parse all available events, but only once, to avoid starvation */ + if (ecb_expect_true (tail > head)) /* normal case around */ + linuxaio_parse_events (EV_A_ ring->io_events + head, tail - head); + else /* wrapped around */ + { + linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head); + linuxaio_parse_events (EV_A_ ring->io_events, tail); + } + + ECB_MEMORY_FENCE_RELEASE; + /* as an extension to C, we hope that the volatile will make this atomic and once-only */ + *(volatile unsigned *)&ring->head = tail; + + return 1; +} + +inline_size +int +linuxaio_ringbuf_valid (EV_P) +{ + struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx; + + return ecb_expect_true (ring->magic == AIO_RING_MAGIC) + && ring->incompat_features == EV_AIO_RING_INCOMPAT_FEATURES + && ring->header_length == sizeof (struct aio_ring); /* TODO: or use it to find io_event[0]? */ +} + +/* read at least one event from kernel, or timeout */ +inline_size +void +linuxaio_get_events (EV_P_ ev_tstamp timeout) +{ + struct timespec ts; + struct io_event ioev[8]; /* 256 octet stack space */ + int want = 1; /* how many events to request */ + int ringbuf_valid = linuxaio_ringbuf_valid (EV_A); + + if (ecb_expect_true (ringbuf_valid)) + { + /* if the ring buffer has any events, we don't wait or call the kernel at all */ + if (linuxaio_get_events_from_ring (EV_A)) + return; + + /* if the ring buffer is empty, and we don't have a timeout, then don't call the kernel */ + if (!timeout) + return; + } + else + /* no ringbuffer, request slightly larger batch */ + want = sizeof (ioev) / sizeof (ioev [0]); + + /* no events, so wait for some + * for fairness reasons, we do this in a loop, to fetch all events + */ + for (;;) + { + int res; + + EV_RELEASE_CB; + + EV_TS_SET (ts, timeout); + res = evsys_io_getevents (linuxaio_ctx, 1, want, ioev, &ts); + + EV_ACQUIRE_CB; + + if (res < 0) + if (errno == EINTR) + /* ignored, retry */; + else + ev_syserr ("(libev) linuxaio io_getevents"); + else if (res) + { + /* at least one event available, handle them */ + linuxaio_parse_events (EV_A_ ioev, res); + + if (ecb_expect_true (ringbuf_valid)) + { + /* if we have a ring buffer, handle any remaining events in it */ + linuxaio_get_events_from_ring (EV_A); + + /* at this point, we should have handled all outstanding events */ + break; + } + else if (res < want) + /* otherwise, if there were fewere events than we wanted, we assume there are no more */ + break; + } + else + break; /* no events from the kernel, we are done */ + + timeout = EV_TS_CONST (0.); /* only wait in the first iteration */ + } +} + +inline_size +int +linuxaio_io_setup (EV_P) +{ + linuxaio_ctx = 0; + return evsys_io_setup (linuxaio_nr_events (EV_A), &linuxaio_ctx); +} + +static void +linuxaio_poll (EV_P_ ev_tstamp timeout) +{ + int submitted; + + /* first phase: submit new iocbs */ + + /* io_submit might return less than the requested number of iocbs */ + /* this is, afaics, only because of errors, but we go by the book and use a loop, */ + /* which allows us to pinpoint the erroneous iocb */ + for (submitted = 0; submitted < linuxaio_submitcnt; ) + { + int res = evsys_io_submit (linuxaio_ctx, linuxaio_submitcnt - submitted, linuxaio_submits + submitted); + + if (ecb_expect_false (res < 0)) + if (errno == EINVAL) + { + /* This happens for unsupported fds, officially, but in my testing, + * also randomly happens for supported fds. We fall back to good old + * poll() here, under the assumption that this is a very rare case. + * See https://lore.kernel.org/patchwork/patch/1047453/ to see + * discussion about such a case (ttys) where polling for POLLIN + * fails but POLLIN|POLLOUT works. + */ + struct iocb *iocb = linuxaio_submits [submitted]; + epoll_modify (EV_A_ iocb->aio_fildes, 0, anfds [iocb->aio_fildes].events); + iocb->aio_reqprio = -1; /* mark iocb as epoll */ + + res = 1; /* skip this iocb - another iocb, another chance */ + } + else if (errno == EAGAIN) + { + /* This happens when the ring buffer is full, or some other shit we + * don't know and isn't documented. Most likely because we have too + * many requests and linux aio can't be assed to handle them. + * In this case, we try to allocate a larger ring buffer, freeing + * ours first. This might fail, in which case we have to fall back to 100% + * epoll. + * God, how I hate linux not getting its act together. Ever. + */ + evsys_io_destroy (linuxaio_ctx); + linuxaio_submitcnt = 0; + + /* rearm all fds with active iocbs */ + { + int fd; + for (fd = 0; fd < linuxaio_iocbpmax; ++fd) + if (linuxaio_iocbps [fd]->io.aio_buf) + linuxaio_fd_rearm (EV_A_ fd); + } + + ++linuxaio_iteration; + if (linuxaio_io_setup (EV_A) < 0) + { + /* TODO: rearm all and recreate epoll backend from scratch */ + /* TODO: might be more prudent? */ + + /* to bad, we can't get a new aio context, go 100% epoll */ + linuxaio_free_iocbp (EV_A); + ev_io_stop (EV_A_ &linuxaio_epoll_w); + ev_ref (EV_A); + linuxaio_ctx = 0; + + backend = EVBACKEND_EPOLL; + backend_modify = epoll_modify; + backend_poll = epoll_poll; + } + + timeout = EV_TS_CONST (0.); + /* it's easiest to handle this mess in another iteration */ + return; + } + else if (errno == EBADF) + { + assert (("libev: event loop rejected bad fd", errno != EBADF)); + fd_kill (EV_A_ linuxaio_submits [submitted]->aio_fildes); + + res = 1; /* skip this iocb */ + } + else if (errno == EINTR) /* not seen in reality, not documented */ + res = 0; /* silently ignore and retry */ + else + { + ev_syserr ("(libev) linuxaio io_submit"); + res = 0; + } + + submitted += res; + } + + linuxaio_submitcnt = 0; + + /* second phase: fetch and parse events */ + + linuxaio_get_events (EV_A_ timeout); +} + +inline_size +int +linuxaio_init (EV_P_ int flags) +{ + /* would be great to have a nice test for IOCB_CMD_POLL instead */ + /* also: test some semi-common fd types, such as files and ttys in recommended_backends */ + /* 4.18 introduced IOCB_CMD_POLL, 4.19 made epoll work, and we need that */ + if (ev_linux_version () < 0x041300) + return 0; + + if (!epoll_init (EV_A_ 0)) + return 0; + + linuxaio_iteration = 0; + + if (linuxaio_io_setup (EV_A) < 0) + { + epoll_destroy (EV_A); + return 0; + } + + ev_io_init (&linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ); + ev_set_priority (&linuxaio_epoll_w, EV_MAXPRI); + ev_io_start (EV_A_ &linuxaio_epoll_w); + ev_unref (EV_A); /* watcher should not keep loop alive */ + + backend_modify = linuxaio_modify; + backend_poll = linuxaio_poll; + + linuxaio_iocbpmax = 0; + linuxaio_iocbps = 0; + + linuxaio_submits = 0; + linuxaio_submitmax = 0; + linuxaio_submitcnt = 0; + + return EVBACKEND_LINUXAIO; +} + +inline_size +void +linuxaio_destroy (EV_P) +{ + epoll_destroy (EV_A); + linuxaio_free_iocbp (EV_A); + evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */ +} + +ecb_cold +static void +linuxaio_fork (EV_P) +{ + linuxaio_submitcnt = 0; /* all pointers were invalidated */ + linuxaio_free_iocbp (EV_A); /* this frees all iocbs, which is very heavy-handed */ + evsys_io_destroy (linuxaio_ctx); /* fails in child, aio context is destroyed */ + + linuxaio_iteration = 0; /* we start over in the child */ + + while (linuxaio_io_setup (EV_A) < 0) + ev_syserr ("(libev) linuxaio io_setup"); + + /* forking epoll should also effectively unregister all fds from the backend */ + epoll_fork (EV_A); + /* epoll_fork already did this. hopefully */ + /*fd_rearm_all (EV_A);*/ + + ev_io_stop (EV_A_ &linuxaio_epoll_w); + ev_io_set (EV_A_ &linuxaio_epoll_w, backend_fd, EV_READ); + ev_io_start (EV_A_ &linuxaio_epoll_w); +} + |