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Edit File: ev_iouring.c
/* * libev linux io_uring fd activity backend * * Copyright (c) 2019-2020 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 two mmaps instead of one? one would be more space-efficient, * and I can't see what benefit two would have (other than being * somehow resizable/relocatable, but that's apparently not possible). * f) hmm, it's practically undebuggable (gdb can't access the memory, and * the bizarre way structure offsets are communicated 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. * (from what I gather from the author Jens Axboe, it simply didn't * occur to him, and he made good on it by adding an unlimited nuber * of timeouts later :). * h) initially there was a hardcoded limit of 4096 outstanding events. * later versions not only bump this to 32k, but also can handle * an unlimited amount of events, so this only affects the batch size. * i) unlike linux aio, you *can* register more then the limit * of fd events. while early verisons of io_uring signalled an overflow * and you ended up getting wet. 5.5+ does not do this anymore. * j) but, oh my! it had exactly the same bugs as the linux aio backend, * where some undocumented poll combinations just fail. fortunately, * after finally reaching the author, he was more than willing to fix * this probably in 5.6+. * k) overall, the *API* itself is, I dare to say, not a total trainwreck. * once the bugs ae fixed (probably in 5.6+), it will be without * competition. */ /* TODO: use internal TIMEOUT */ /* TODO: take advantage of single mmap, NODROP etc. */ /* TODO: resize cq/sq size independently */ #include <sys/timerfd.h> #include <sys/mman.h> #include <poll.h> #include <stdint.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; union { __u64 off; __u64 addr2; }; __u64 addr; __u32 len; union { __kernel_rwf_t rw_flags; __u32 fsync_flags; __u16 poll_events; __u32 sync_range_flags; __u32 msg_flags; __u32 timeout_flags; __u32 accept_flags; __u32 cancel_flags; __u32 open_flags; __u32 statx_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 features; __u32 resv[4]; struct io_sqring_offsets sq_off; struct io_cqring_offsets cq_off; }; #define IORING_SETUP_CQSIZE 0x00000008 #define IORING_OP_POLL_ADD 6 #define IORING_OP_POLL_REMOVE 7 #define IORING_OP_TIMEOUT 11 #define IORING_OP_TIMEOUT_REMOVE 12 /* relative or absolute, reference clock is CLOCK_MONOTONIC */ struct iouring_kernel_timespec { int64_t tv_sec; long long tv_nsec; }; #define IORING_TIMEOUT_ABS 0x00000001 #define IORING_ENTER_GETEVENTS 0x01 #define IORING_OFF_SQ_RING 0x00000000ULL #define IORING_OFF_CQ_RING 0x08000000ULL #define IORING_OFF_SQES 0x10000000ULL #define IORING_FEAT_SINGLE_MMAP 0x00000001 #define IORING_FEAT_NODROP 0x00000002 #define IORING_FEAT_SUBMIT_STABLE 0x00000004 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)) inline_speed int iouring_enter (EV_P_ ev_tstamp timeout) { 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); assert (("libev: io_uring_enter did not consume all sqes", (res < 0 || res == iouring_to_submit))); iouring_to_submit = 0; EV_ACQUIRE_CB; return res; } /* TODO: can we move things around so we don't need this forward-reference? */ static void iouring_poll (EV_P_ ev_tstamp timeout); static struct io_uring_sqe * iouring_sqe_get (EV_P) { unsigned tail; for (;;) { tail = EV_SQ_VAR (tail); if (ecb_expect_true (tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries))) break; /* whats the problem, we have free sqes */ /* queue full, need to flush and possibly handle some events */ #if EV_FEATURE_CODE /* first we ask the kernel nicely, most often this frees up some sqes */ int res = iouring_enter (EV_A_ EV_TS_CONST (0.)); ECB_MEMORY_FENCE_ACQUIRE; /* better safe than sorry */ if (res >= 0) continue; /* yes, it worked, try again */ #endif /* some problem, possibly EBUSY - do the full poll and let it handle any issues */ iouring_poll (EV_A_ EV_TS_CONST (0.)); /* iouring_poll should have done ECB_MEMORY_FENCE_ACQUIRE for us */ } /*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 void 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; } /* called for full and partial cleanup */ ecb_cold static void 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_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; if (!have_monotonic) /* cannot really happen, but what if11 */ return -1; for (;;) { iouring_fd = evsys_io_uring_setup (iouring_entries, ¶ms); if (iouring_fd >= 0) break; /* yippie */ if (errno != EINVAL) return -1; /* we failed */ #if TODO if ((~params.features) & (IORING_FEAT_NODROP | IORING_FEATURE_SINGLE_MMAP | IORING_FEAT_SUBMIT_STABLE)) return -1; /* we require the above features */ #endif /* 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"); fd_rearm_all (EV_A); 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 (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; /* Jens Axboe notified me that user_data is not what is documented, but is * some kind of unique ID that has to match, otherwise the request cannot * be removed. Since we don't *really* have that, we pass in the old * generation counter - if that fails, too bad, it will hopefully be removed * at close time and then be ignored. */ sqe->addr = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32); sqe->user_data = (uint64_t)-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->addr = 0; 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; /* user_data -1 is a remove that we are not atm. interested in */ if (cqe->user_data == (uint64_t)-1) return; 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 */ /* other than skipping removal events, */ /* this should actually be very rare */ if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen)) return; if (ecb_expect_false (res < 0)) { /*TODO: EINVAL handling (was something failed with this fd)*/ 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 the 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. * TODO: is this necessary with newer kernels? */ 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 */ /* we also clar the timeout if there are outstanding fdchanges */ /* the latter should only happen if both the sq and cq are full, most likely */ /* because we have a lot of event sources that immediately complete */ /* TODO: fdchacngecnt is always 0 because fd_reify does not have two buffers yet */ if (iouring_handle_cq (EV_A) || fdchangecnt) 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 = iouring_enter (EV_A_ timeout); if (ecb_expect_false (res < 0)) if (errno == EINTR) /* ignore */; else if (errno == EBUSY) /* cq full, cannot submit - should be rare because we flush the cq first, so simply ignore */; else ev_syserr ("(libev) iouring setup"); else iouring_handle_cq (EV_A); } } inline_size int iouring_init (EV_P_ int flags) { 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_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ); ev_set_priority (&iouring_tfd_w, EV_MINPRI); 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); }