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Diffstat (limited to 'libev/ev_iouring.c')
| -rw-r--r-- | libev/ev_iouring.c | 645 |
1 files changed, 645 insertions, 0 deletions
diff --git a/libev/ev_iouring.c b/libev/ev_iouring.c new file mode 100644 index 0000000..b80ab0e --- /dev/null +++ b/libev/ev_iouring.c @@ -0,0 +1,645 @@ +/* + * libev linux io_uring 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 io_uring: + * + * a) it's the best interface I have seen so far. on linux. + * b) best is not necessarily very good. + * c) it's better than the aio mess, doesn't suffer from the fork problems + * of linux aio or epoll and so on and so on. and you could do event stuff + * without any syscalls. what's not to like? + * d) ok, it's vastly more complex, but that's ok, really. + * e) why 3 mmaps instead of one? one would be more space-efficient, + * and I can't see what benefit three would have (other than being + * somehow resizable/relocatable, but that's apparently not possible). + * f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and + the bizarre way structure offsets are commuinicated makes it hard to + * just print the ring buffer heads, even *iff* the memory were visible + * in gdb. but then, that's also ok, really. + * g) well, you cannot specify a timeout when waiting for events. no, + * seriously, the interface doesn't support a timeout. never seen _that_ + * before. sure, you can use a timerfd, but that's another syscall + * you could have avoided. overall, this bizarre omission smells + * like a µ-optimisation by the io_uring author for his personal + * applications, to the detriment of everybody else who just wants + * an event loop. but, umm, ok, if that's all, it could be worse. + * h) there is a hardcoded limit of 4096 outstanding events. okay, + * at least there is no arbitrary low system-wide limit... + * i) unlike linux aio, you *can* register more then the limit + * of fd events, and the kernel will "gracefully" signal an + * overflow, after which you could destroy and recreate the kernel + * state, a bit bigger, or fall back to e.g. poll. thats not + * totally insane, but kind of questions the point a high + * performance I/O framework when it doesn't really work + * under stress. + * j) but, oh my! is has exactly the same bugs as the linux aio backend, + * where some undocumented poll combinations just fail. + * so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course, + * this is completely undocumented, have I mantioned this already? + * k) overall, the *API* itself is, I dare to say, not a total trainwreck. + * the big isuess with it are the bugs requiring epoll, which might + * or might not get fixed (do I hold my breath?). + */ + +#include <sys/timerfd.h> +#include <sys/mman.h> +#include <poll.h> + +#define IOURING_INIT_ENTRIES 32 + +/*****************************************************************************/ +/* syscall wrapdadoop - this section has the raw api/abi definitions */ + +#include <linux/fs.h> +#include <linux/types.h> + +/* mostly directly taken from the kernel or documentation */ + +struct io_uring_sqe +{ + __u8 opcode; + __u8 flags; + __u16 ioprio; + __s32 fd; + __u64 off; + __u64 addr; + __u32 len; + union { + __kernel_rwf_t rw_flags; + __u32 fsync_flags; + __u16 poll_events; + __u32 sync_range_flags; + __u32 msg_flags; + }; + __u64 user_data; + union { + __u16 buf_index; + __u64 __pad2[3]; + }; +}; + +struct io_uring_cqe +{ + __u64 user_data; + __s32 res; + __u32 flags; +}; + +struct io_sqring_offsets +{ + __u32 head; + __u32 tail; + __u32 ring_mask; + __u32 ring_entries; + __u32 flags; + __u32 dropped; + __u32 array; + __u32 resv1; + __u64 resv2; +}; + +struct io_cqring_offsets +{ + __u32 head; + __u32 tail; + __u32 ring_mask; + __u32 ring_entries; + __u32 overflow; + __u32 cqes; + __u64 resv[2]; +}; + +struct io_uring_params +{ + __u32 sq_entries; + __u32 cq_entries; + __u32 flags; + __u32 sq_thread_cpu; + __u32 sq_thread_idle; + __u32 resv[5]; + struct io_sqring_offsets sq_off; + struct io_cqring_offsets cq_off; +}; + +#define IORING_OP_POLL_ADD 6 +#define IORING_OP_POLL_REMOVE 7 + +#define IORING_ENTER_GETEVENTS 0x01 + +#define IORING_OFF_SQ_RING 0x00000000ULL +#define IORING_OFF_CQ_RING 0x08000000ULL +#define IORING_OFF_SQES 0x10000000ULL + +inline_size +int +evsys_io_uring_setup (unsigned entries, struct io_uring_params *params) +{ + return ev_syscall2 (SYS_io_uring_setup, entries, params); +} + +inline_size +int +evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz) +{ + return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz); +} + +/*****************************************************************************/ +/* actual backed implementation */ + +/* we hope that volatile will make the compiler access this variables only once */ +#define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name) +#define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name) + +/* the index array */ +#define EV_SQ_ARRAY ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array)) + +/* the submit/completion queue entries */ +#define EV_SQES ((struct io_uring_sqe *) iouring_sqes) +#define EV_CQES ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes)) + +static +struct io_uring_sqe * +iouring_sqe_get (EV_P) +{ + unsigned tail = EV_SQ_VAR (tail); + + if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries)) + { + /* queue full, flush */ + evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0); + iouring_to_submit = 0; + } + + assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries))); + + return EV_SQES + (tail & EV_SQ_VAR (ring_mask)); +} + +inline_size +struct io_uring_sqe * +iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe) +{ + unsigned idx = sqe - EV_SQES; + + EV_SQ_ARRAY [idx] = idx; + ECB_MEMORY_FENCE_RELEASE; + ++EV_SQ_VAR (tail); + /*ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */ + ++iouring_to_submit; +} + +/*****************************************************************************/ + +/* when the timerfd expires we simply note the fact, + * as the purpose of the timerfd is to wake us up, nothing else. + * the next iteration should re-set it. + */ +static void +iouring_tfd_cb (EV_P_ struct ev_io *w, int revents) +{ + iouring_tfd_to = EV_TSTAMP_HUGE; +} + +static void +iouring_epoll_cb (EV_P_ struct ev_io *w, int revents) +{ + epoll_poll (EV_A_ 0); +} + +/* called for full and partial cleanup */ +ecb_cold +static int +iouring_internal_destroy (EV_P) +{ + close (iouring_tfd); + close (iouring_fd); + + if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size); + if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size); + if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size ); + + if (ev_is_active (&iouring_epoll_w)) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_epoll_w); + if (ev_is_active (&iouring_tfd_w )) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_tfd_w ); +} + +ecb_cold +static int +iouring_internal_init (EV_P) +{ + struct io_uring_params params = { 0 }; + + iouring_to_submit = 0; + + iouring_tfd = -1; + iouring_sq_ring = MAP_FAILED; + iouring_cq_ring = MAP_FAILED; + iouring_sqes = MAP_FAILED; + + for (;;) + { + iouring_fd = evsys_io_uring_setup (iouring_entries, ¶ms); + + if (iouring_fd >= 0) + break; /* yippie */ + + if (errno != EINVAL) + return -1; /* we failed */ + + /* EINVAL: lots of possible reasons, but maybe + * it is because we hit the unqueryable hardcoded size limit + */ + + /* we hit the limit already, give up */ + if (iouring_max_entries) + return -1; + + /* first time we hit EINVAL? assume we hit the limit, so go back and retry */ + iouring_entries >>= 1; + iouring_max_entries = iouring_entries; + } + + iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned); + iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe); + iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe); + + iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE, + MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING); + iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE, + MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING); + iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE, + MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES); + + if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED) + return -1; + + iouring_sq_head = params.sq_off.head; + iouring_sq_tail = params.sq_off.tail; + iouring_sq_ring_mask = params.sq_off.ring_mask; + iouring_sq_ring_entries = params.sq_off.ring_entries; + iouring_sq_flags = params.sq_off.flags; + iouring_sq_dropped = params.sq_off.dropped; + iouring_sq_array = params.sq_off.array; + + iouring_cq_head = params.cq_off.head; + iouring_cq_tail = params.cq_off.tail; + iouring_cq_ring_mask = params.cq_off.ring_mask; + iouring_cq_ring_entries = params.cq_off.ring_entries; + iouring_cq_overflow = params.cq_off.overflow; + iouring_cq_cqes = params.cq_off.cqes; + + iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC); + + if (iouring_tfd < 0) + return iouring_tfd; + + iouring_tfd_to = EV_TSTAMP_HUGE; + + return 0; +} + +ecb_cold +static void +iouring_fork (EV_P) +{ + iouring_internal_destroy (EV_A); + + while (iouring_internal_init (EV_A) < 0) + ev_syserr ("(libev) io_uring_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_ &iouring_epoll_w); + ev_io_set (EV_A_ &iouring_epoll_w, backend_fd, EV_READ); + ev_io_start (EV_A_ &iouring_epoll_w); + + ev_io_stop (EV_A_ &iouring_tfd_w); + ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ); + ev_io_start (EV_A_ &iouring_tfd_w); +} + +/*****************************************************************************/ + +static void +iouring_modify (EV_P_ int fd, int oev, int nev) +{ + if (ecb_expect_false (anfds [fd].eflags)) + { + /* 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 (iouring_fd, EPOLL_CTL_DEL, fd, 0); + anfds [fd].eflags = 0; + oev = 0; + } + + if (oev) + { + /* we assume the sqe's are all "properly" initialised */ + struct io_uring_sqe *sqe = iouring_sqe_get (EV_A); + sqe->opcode = IORING_OP_POLL_REMOVE; + sqe->fd = fd; + sqe->user_data = -1; + iouring_sqe_submit (EV_A_ sqe); + + /* increment generation counter to avoid handling old events */ + ++anfds [fd].egen; + } + + if (nev) + { + struct io_uring_sqe *sqe = iouring_sqe_get (EV_A); + sqe->opcode = IORING_OP_POLL_ADD; + sqe->fd = fd; + sqe->user_data = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32); + sqe->poll_events = + (nev & EV_READ ? POLLIN : 0) + | (nev & EV_WRITE ? POLLOUT : 0); + iouring_sqe_submit (EV_A_ sqe); + } +} + +inline_size +void +iouring_tfd_update (EV_P_ ev_tstamp timeout) +{ + ev_tstamp tfd_to = mn_now + timeout; + + /* we assume there will be many iterations per timer change, so + * we only re-set the timerfd when we have to because its expiry + * is too late. + */ + if (ecb_expect_false (tfd_to < iouring_tfd_to)) + { + struct itimerspec its; + + iouring_tfd_to = tfd_to; + EV_TS_SET (its.it_interval, 0.); + EV_TS_SET (its.it_value, tfd_to); + + if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0) + assert (("libev: iouring timerfd_settime failed", 0)); + } +} + +inline_size +void +iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe) +{ + int fd = cqe->user_data & 0xffffffffU; + uint32_t gen = cqe->user_data >> 32; + int res = cqe->res; + + /* ignore fd removal events, if there are any. TODO: verify */ + if (cqe->user_data == (__u64)-1) + abort ();//D + + assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax)); + + /* documentation lies, of course. the result value is NOT like + * normal syscalls, but like linux raw syscalls, i.e. negative + * error numbers. fortunate, as otherwise there would be no way + * to get error codes at all. still, why not document this? + */ + + /* ignore event if generation doesn't match */ + /* this should actually be very rare */ + if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen)) + return; + + if (ecb_expect_false (res < 0)) + { + if (res == -EINVAL) + { + /* we assume this error code means the fd/poll combination is buggy + * and fall back to epoll. + * this error code might also indicate a bug, but the kernel doesn't + * distinguish between those two conditions, so... sigh... + */ + + epoll_modify (EV_A_ fd, 0, anfds [fd].events); + } + else if (res == -EBADF) + { + assert (("libev: event loop rejected bad fd", res != -EBADF)); + fd_kill (EV_A_ fd); + } + else + { + errno = -res; + ev_syserr ("(libev) IORING_OP_POLL_ADD"); + } + + return; + } + + /* 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) + ); + + /* io_uring is oneshot, so we need to re-arm the fd next iteration */ + /* this also means we usually have to do at least one syscall per iteration */ + anfds [fd].events = 0; + fd_change (EV_A_ fd, EV_ANFD_REIFY); +} + +/* called when the event queue overflows */ +ecb_cold +static void +iouring_overflow (EV_P) +{ + /* we have two options, resize the queue (by tearing down + * everything and recreating it, or living with it + * and polling. + * we implement this by resizing tghe queue, and, if that fails, + * we just recreate the state on every failure, which + * kind of is a very inefficient poll. + * one danger is, due to the bios toward lower fds, + * we will only really get events for those, so + * maybe we need a poll() fallback, after all. + */ + /*EV_CQ_VAR (overflow) = 0;*/ /* need to do this if we keep the state and poll manually */ + + fd_rearm_all (EV_A); + + /* we double the size until we hit the hard-to-probe maximum */ + if (!iouring_max_entries) + { + iouring_entries <<= 1; + iouring_fork (EV_A); + } + else + { + /* we hit the kernel limit, we should fall back to something else. + * we can either poll() a few times and hope for the best, + * poll always, or switch to epoll. + * since we use epoll anyways, go epoll. + */ + + iouring_internal_destroy (EV_A); + + /* this should make it so that on return, we don'T call any uring functions */ + iouring_to_submit = 0; + + for (;;) + { + backend = epoll_init (EV_A_ 0); + + if (backend) + break; + + ev_syserr ("(libev) iouring switch to epoll"); + } + } +} + +/* handle any events in the completion queue, return true if there were any */ +static int +iouring_handle_cq (EV_P) +{ + unsigned head, tail, mask; + + head = EV_CQ_VAR (head); + ECB_MEMORY_FENCE_ACQUIRE; + tail = EV_CQ_VAR (tail); + + if (head == tail) + return 0; + + /* it can only overflow if we have events, yes, yes? */ + if (ecb_expect_false (EV_CQ_VAR (overflow))) + { + iouring_overflow (EV_A); + return 1; + } + + mask = EV_CQ_VAR (ring_mask); + + do + iouring_process_cqe (EV_A_ &EV_CQES [head++ & mask]); + while (head != tail); + + EV_CQ_VAR (head) = head; + ECB_MEMORY_FENCE_RELEASE; + + return 1; +} + +static void +iouring_poll (EV_P_ ev_tstamp timeout) +{ + /* if we have events, no need for extra syscalls, but we might have to queue events */ + if (iouring_handle_cq (EV_A)) + timeout = EV_TS_CONST (0.); + else + /* no events, so maybe wait for some */ + iouring_tfd_update (EV_A_ timeout); + + /* only enter the kernel if we have something to submit, or we need to wait */ + if (timeout || iouring_to_submit) + { + int res; + + EV_RELEASE_CB; + + res = evsys_io_uring_enter (iouring_fd, iouring_to_submit, 1, + timeout > EV_TS_CONST (0.) ? IORING_ENTER_GETEVENTS : 0, 0, 0); + iouring_to_submit = 0; + + EV_ACQUIRE_CB; + + if (ecb_expect_false (res < 0)) + if (errno == EINTR) + /* ignore */; + else + ev_syserr ("(libev) iouring setup"); + else + iouring_handle_cq (EV_A); + } +} + +inline_size +int +iouring_init (EV_P_ int flags) +{ + if (!epoll_init (EV_A_ 0)) + return 0; + + iouring_entries = IOURING_INIT_ENTRIES; + iouring_max_entries = 0; + + if (iouring_internal_init (EV_A) < 0) + { + iouring_internal_destroy (EV_A); + return 0; + } + + ev_io_init (&iouring_epoll_w, iouring_epoll_cb, backend_fd, EV_READ); + ev_set_priority (&iouring_epoll_w, EV_MAXPRI); + + ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ); + ev_set_priority (&iouring_tfd_w, EV_MAXPRI); + + ev_io_start (EV_A_ &iouring_epoll_w); + ev_unref (EV_A); /* watcher should not keep loop alive */ + + ev_io_start (EV_A_ &iouring_tfd_w); + ev_unref (EV_A); /* watcher should not keep loop alive */ + + backend_modify = iouring_modify; + backend_poll = iouring_poll; + + return EVBACKEND_IOURING; +} + +inline_size +void +iouring_destroy (EV_P) +{ + iouring_internal_destroy (EV_A); + epoll_destroy (EV_A); +} + |