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649 lines
19 KiB
C
649 lines
19 KiB
C
/*
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* libev linux io_uring fd activity backend
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*
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* Copyright (c) 2019 Marc Alexander Lehmann <libev@schmorp.de>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without modifica-
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* tion, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MER-
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* CHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
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* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPE-
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* CIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTH-
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* ERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Alternatively, the contents of this file may be used under the terms of
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* the GNU General Public License ("GPL") version 2 or any later version,
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* in which case the provisions of the GPL are applicable instead of
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* the above. If you wish to allow the use of your version of this file
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* only under the terms of the GPL and not to allow others to use your
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* version of this file under the BSD license, indicate your decision
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* by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL. If you do not delete the
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* provisions above, a recipient may use your version of this file under
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* either the BSD or the GPL.
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*/
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/*
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* general notes about linux io_uring:
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*
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* a) it's the best interface I have seen so far. on linux.
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* b) best is not necessarily very good.
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* c) it's better than the aio mess, doesn't suffer from the fork problems
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* of linux aio or epoll and so on and so on. and you could do event stuff
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* without any syscalls. what's not to like?
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* d) ok, it's vastly more complex, but that's ok, really.
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* e) why 3 mmaps instead of one? one would be more space-efficient,
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* and I can't see what benefit three would have (other than being
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* somehow resizable/relocatable, but that's apparently not possible).
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* f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and
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the bizarre way structure offsets are commuinicated makes it hard to
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* just print the ring buffer heads, even *iff* the memory were visible
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* in gdb. but then, that's also ok, really.
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* g) well, you cannot specify a timeout when waiting for events. no,
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* seriously, the interface doesn't support a timeout. never seen _that_
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* before. sure, you can use a timerfd, but that's another syscall
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* you could have avoided. overall, this bizarre omission smells
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* like a µ-optimisation by the io_uring author for his personal
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* applications, to the detriment of everybody else who just wants
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* an event loop. but, umm, ok, if that's all, it could be worse.
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* h) there is a hardcoded limit of 4096 outstanding events. okay,
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* at least there is no arbitrary low system-wide limit...
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* i) unlike linux aio, you *can* register more then the limit
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* of fd events, and the kernel will "gracefully" signal an
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* overflow, after which you could destroy and recreate the kernel
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* state, a bit bigger, or fall back to e.g. poll. thats not
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* totally insane, but kind of questions the point a high
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* performance I/O framework when it doesn't really work
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* under stress.
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* j) but, oh my! is has exactly the same bugs as the linux aio backend,
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* where some undocumented poll combinations just fail.
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* so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course,
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* this is completely undocumented, have I mantioned this already?
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* k) overall, the *API* itself is, I dare to say, not a total trainwreck.
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* the big isuess with it are the bugs requiring epoll, which might
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* or might not get fixed (do I hold my breath?).
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*/
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#include <sys/timerfd.h>
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#include <sys/mman.h>
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#include <poll.h>
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#define IOURING_INIT_ENTRIES 32
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/*****************************************************************************/
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/* syscall wrapdadoop - this section has the raw api/abi definitions */
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#include <linux/fs.h>
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#include <linux/types.h>
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/* mostly directly taken from the kernel or documentation */
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struct io_uring_sqe
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{
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__u8 opcode;
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__u8 flags;
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__u16 ioprio;
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__s32 fd;
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__u64 off;
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__u64 addr;
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__u32 len;
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union {
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__kernel_rwf_t rw_flags;
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__u32 fsync_flags;
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__u16 poll_events;
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__u32 sync_range_flags;
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__u32 msg_flags;
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};
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__u64 user_data;
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union {
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__u16 buf_index;
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__u64 __pad2[3];
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};
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};
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struct io_uring_cqe
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{
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__u64 user_data;
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__s32 res;
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__u32 flags;
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};
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struct io_sqring_offsets
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{
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__u32 head;
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__u32 tail;
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__u32 ring_mask;
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__u32 ring_entries;
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__u32 flags;
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__u32 dropped;
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__u32 array;
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__u32 resv1;
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__u64 resv2;
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};
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struct io_cqring_offsets
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{
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__u32 head;
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__u32 tail;
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__u32 ring_mask;
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__u32 ring_entries;
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__u32 overflow;
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__u32 cqes;
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__u64 resv[2];
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};
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struct io_uring_params
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{
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__u32 sq_entries;
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__u32 cq_entries;
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__u32 flags;
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__u32 sq_thread_cpu;
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__u32 sq_thread_idle;
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__u32 resv[5];
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struct io_sqring_offsets sq_off;
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struct io_cqring_offsets cq_off;
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};
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#define IORING_OP_POLL_ADD 6
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#define IORING_OP_POLL_REMOVE 7
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#define IORING_ENTER_GETEVENTS 0x01
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#define IORING_OFF_SQ_RING 0x00000000ULL
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#define IORING_OFF_CQ_RING 0x08000000ULL
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#define IORING_OFF_SQES 0x10000000ULL
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inline_size
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int
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evsys_io_uring_setup (unsigned entries, struct io_uring_params *params)
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{
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return ev_syscall2 (SYS_io_uring_setup, entries, params);
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}
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inline_size
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int
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evsys_io_uring_enter (int fd, unsigned to_submit, unsigned min_complete, unsigned flags, const sigset_t *sig, size_t sigsz)
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{
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return ev_syscall6 (SYS_io_uring_enter, fd, to_submit, min_complete, flags, sig, sigsz);
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}
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/*****************************************************************************/
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/* actual backed implementation */
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/* we hope that volatile will make the compiler access this variables only once */
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#define EV_SQ_VAR(name) *(volatile unsigned *)((char *)iouring_sq_ring + iouring_sq_ ## name)
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#define EV_CQ_VAR(name) *(volatile unsigned *)((char *)iouring_cq_ring + iouring_cq_ ## name)
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/* the index array */
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#define EV_SQ_ARRAY ((unsigned *)((char *)iouring_sq_ring + iouring_sq_array))
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/* the submit/completion queue entries */
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#define EV_SQES ((struct io_uring_sqe *) iouring_sqes)
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#define EV_CQES ((struct io_uring_cqe *)((char *)iouring_cq_ring + iouring_cq_cqes))
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static
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struct io_uring_sqe *
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iouring_sqe_get (EV_P)
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{
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unsigned tail = EV_SQ_VAR (tail);
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if (tail + 1 - EV_SQ_VAR (head) > EV_SQ_VAR (ring_entries))
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{
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/* queue full, flush */
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evsys_io_uring_enter (iouring_fd, iouring_to_submit, 0, 0, 0, 0);
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iouring_to_submit = 0;
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}
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assert (("libev: io_uring queue full after flush", tail + 1 - EV_SQ_VAR (head) <= EV_SQ_VAR (ring_entries)));
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return EV_SQES + (tail & EV_SQ_VAR (ring_mask));
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}
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inline_size
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struct io_uring_sqe *
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iouring_sqe_submit (EV_P_ struct io_uring_sqe *sqe)
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{
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unsigned idx = sqe - EV_SQES;
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EV_SQ_ARRAY [idx] = idx;
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ECB_MEMORY_FENCE_RELEASE;
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++EV_SQ_VAR (tail);
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/*ECB_MEMORY_FENCE_RELEASE; /* for the time being we assume this is not needed */
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++iouring_to_submit;
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}
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/*****************************************************************************/
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/* when the timerfd expires we simply note the fact,
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* as the purpose of the timerfd is to wake us up, nothing else.
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* the next iteration should re-set it.
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*/
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static void
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iouring_tfd_cb (EV_P_ struct ev_io *w, int revents)
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{
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iouring_tfd_to = EV_TSTAMP_HUGE;
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}
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static void
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iouring_epoll_cb (EV_P_ struct ev_io *w, int revents)
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{
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epoll_poll (EV_A_ 0);
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}
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/* called for full and partial cleanup */
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ecb_cold
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static int
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iouring_internal_destroy (EV_P)
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{
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close (iouring_tfd);
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close (iouring_fd);
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if (iouring_sq_ring != MAP_FAILED) munmap (iouring_sq_ring, iouring_sq_ring_size);
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if (iouring_cq_ring != MAP_FAILED) munmap (iouring_cq_ring, iouring_cq_ring_size);
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if (iouring_sqes != MAP_FAILED) munmap (iouring_sqes , iouring_sqes_size );
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if (ev_is_active (&iouring_epoll_w)) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_epoll_w);
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if (ev_is_active (&iouring_tfd_w )) ev_ref (EV_A); ev_io_stop (EV_A_ &iouring_tfd_w );
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}
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ecb_cold
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static int
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iouring_internal_init (EV_P)
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{
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struct io_uring_params params = { 0 };
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iouring_to_submit = 0;
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iouring_tfd = -1;
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iouring_sq_ring = MAP_FAILED;
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iouring_cq_ring = MAP_FAILED;
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iouring_sqes = MAP_FAILED;
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for (;;)
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{
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iouring_fd = evsys_io_uring_setup (iouring_entries, ¶ms);
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if (iouring_fd >= 0)
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break; /* yippie */
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if (errno != EINVAL)
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return -1; /* we failed */
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/* EINVAL: lots of possible reasons, but maybe
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* it is because we hit the unqueryable hardcoded size limit
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*/
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/* we hit the limit already, give up */
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if (iouring_max_entries)
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return -1;
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/* first time we hit EINVAL? assume we hit the limit, so go back and retry */
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iouring_entries >>= 1;
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iouring_max_entries = iouring_entries;
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}
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iouring_sq_ring_size = params.sq_off.array + params.sq_entries * sizeof (unsigned);
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iouring_cq_ring_size = params.cq_off.cqes + params.cq_entries * sizeof (struct io_uring_cqe);
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iouring_sqes_size = params.sq_entries * sizeof (struct io_uring_sqe);
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iouring_sq_ring = mmap (0, iouring_sq_ring_size, PROT_READ | PROT_WRITE,
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MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQ_RING);
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iouring_cq_ring = mmap (0, iouring_cq_ring_size, PROT_READ | PROT_WRITE,
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MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_CQ_RING);
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iouring_sqes = mmap (0, iouring_sqes_size, PROT_READ | PROT_WRITE,
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MAP_SHARED | MAP_POPULATE, iouring_fd, IORING_OFF_SQES);
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if (iouring_sq_ring == MAP_FAILED || iouring_cq_ring == MAP_FAILED || iouring_sqes == MAP_FAILED)
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return -1;
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iouring_sq_head = params.sq_off.head;
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iouring_sq_tail = params.sq_off.tail;
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iouring_sq_ring_mask = params.sq_off.ring_mask;
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iouring_sq_ring_entries = params.sq_off.ring_entries;
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iouring_sq_flags = params.sq_off.flags;
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iouring_sq_dropped = params.sq_off.dropped;
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iouring_sq_array = params.sq_off.array;
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iouring_cq_head = params.cq_off.head;
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iouring_cq_tail = params.cq_off.tail;
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iouring_cq_ring_mask = params.cq_off.ring_mask;
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iouring_cq_ring_entries = params.cq_off.ring_entries;
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iouring_cq_overflow = params.cq_off.overflow;
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iouring_cq_cqes = params.cq_off.cqes;
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iouring_tfd = timerfd_create (CLOCK_MONOTONIC, TFD_CLOEXEC);
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if (iouring_tfd < 0)
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return iouring_tfd;
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iouring_tfd_to = EV_TSTAMP_HUGE;
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return 0;
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}
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ecb_cold
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static void
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iouring_fork (EV_P)
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{
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iouring_internal_destroy (EV_A);
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while (iouring_internal_init (EV_A) < 0)
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ev_syserr ("(libev) io_uring_setup");
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/* forking epoll should also effectively unregister all fds from the backend */
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epoll_fork (EV_A);
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/* epoll_fork already did this. hopefully */
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/*fd_rearm_all (EV_A);*/
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ev_io_stop (EV_A_ &iouring_epoll_w);
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ev_io_set (EV_A_ &iouring_epoll_w, backend_fd, EV_READ);
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ev_io_start (EV_A_ &iouring_epoll_w);
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ev_io_stop (EV_A_ &iouring_tfd_w);
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ev_io_set (EV_A_ &iouring_tfd_w, iouring_tfd, EV_READ);
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ev_io_start (EV_A_ &iouring_tfd_w);
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}
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/*****************************************************************************/
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static void
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iouring_modify (EV_P_ int fd, int oev, int nev)
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{
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fprintf (stderr,"modify %d (%d, %d) %d\n", fd, oev,nev, anfds[fd].eflags);//D
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if (ecb_expect_false (anfds [fd].eflags))
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{
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/* we handed this fd over to epoll, so undo this first */
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/* we do it manually because the optimisations on epoll_modify won't do us any good */
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epoll_ctl (iouring_fd, EPOLL_CTL_DEL, fd, 0);
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anfds [fd].eflags = 0;
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oev = 0;
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}
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if (oev)
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{
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/* we assume the sqe's are all "properly" initialised */
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struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
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sqe->opcode = IORING_OP_POLL_REMOVE;
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sqe->fd = fd;
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sqe->user_data = -1;
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iouring_sqe_submit (EV_A_ sqe);
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/* increment generation counter to avoid handling old events */
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++anfds [fd].egen;
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}
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if (nev)
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{
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struct io_uring_sqe *sqe = iouring_sqe_get (EV_A);
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sqe->opcode = IORING_OP_POLL_ADD;
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sqe->fd = fd;
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sqe->user_data = (uint32_t)fd | ((__u64)(uint32_t)anfds [fd].egen << 32);
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sqe->poll_events =
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(nev & EV_READ ? POLLIN : 0)
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| (nev & EV_WRITE ? POLLOUT : 0);
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iouring_sqe_submit (EV_A_ sqe);
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}
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}
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inline_size
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void
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iouring_tfd_update (EV_P_ ev_tstamp timeout)
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{
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ev_tstamp tfd_to = mn_now + timeout;
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/* we assume there will be many iterations per timer change, so
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* we only re-set the timerfd when we have to because its expiry
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* is too late.
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*/
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if (ecb_expect_false (tfd_to < iouring_tfd_to))
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{
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struct itimerspec its;
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iouring_tfd_to = tfd_to;
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EV_TS_SET (its.it_interval, 0.);
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EV_TS_SET (its.it_value, tfd_to);
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if (timerfd_settime (iouring_tfd, TFD_TIMER_ABSTIME, &its, 0) < 0)
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assert (("libev: iouring timerfd_settime failed", 0));
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}
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}
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inline_size
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void
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iouring_process_cqe (EV_P_ struct io_uring_cqe *cqe)
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{
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int fd = cqe->user_data & 0xffffffffU;
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uint32_t gen = cqe->user_data >> 32;
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int res = cqe->res;
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/* ignore fd removal events, if there are any. TODO: verify */
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if (cqe->user_data == (__u64)-1)
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abort ();//D
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assert (("libev: io_uring fd must be in-bounds", fd >= 0 && fd < anfdmax));
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/* documentation lies, of course. the result value is NOT like
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* normal syscalls, but like linux raw syscalls, i.e. negative
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* error numbers. fortunate, as otherwise there would be no way
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* to get error codes at all. still, why not document this?
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*/
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/* ignore event if generation doesn't match */
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/* this should actually be very rare */
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if (ecb_expect_false (gen != (uint32_t)anfds [fd].egen))
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return;
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if (ecb_expect_false (res < 0))
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{
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if (res == -EINVAL)
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{
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/* we assume this error code means the fd/poll combination is buggy
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* and fall back to epoll.
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* this error code might also indicate a bug, but the kernel doesn't
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* distinguish between those two conditions, so... sigh...
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*/
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epoll_modify (EV_A_ fd, 0, anfds [fd].events);
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}
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else if (res == -EBADF)
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{
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assert (("libev: event loop rejected bad fd", res != -EBADF));
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|
fd_kill (EV_A_ fd);
|
|
}
|
|
else
|
|
{
|
|
errno = -res;
|
|
ev_syserr ("(libev) IORING_OP_POLL_ADD");
|
|
}
|
|
|
|
return;
|
|
}
|
|
|
|
fprintf (stderr, "fd %d event, rearm\n", fd);//D
|
|
|
|
/* 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 = 0.;
|
|
else
|
|
/* no events, so maybe wait for some */
|
|
iouring_tfd_update (EV_A_ timeout);
|
|
|
|
/* only enter the kernel if we have somethign 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 ? 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;
|
|
|
|
ev_io_init (EV_A_ &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);
|
|
|
|
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_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);
|
|
}
|
|
|