On 2/13/2020 3:33 AM, Carter Li 李通洲 wrote: > Thanks for your reply. > > You are right the nop isn't really a good test case. But I actually > found this issue when benchmarking my echo server, which didn't use > NOP of course. If there are no hidden subtle issues in io_uring, your benchmark or the used pattern itself, it's probably because of overhead on async punting (copying iovecs, several extra switches, refcounts, grabbing mm/fs/etc, io-wq itself). I was going to tune async/punting stuff anyway, so I'll look into this. And of course, there is always a good chance Jens have some bright insights BTW, what's benefit of doing poll(fd)->read(fd), but not directly read()? > Test case attached below. Use rust_echo_bench for benchmarking. > https://github.com/haraldh/rust_echo_bench > > > $ gcc link_recv.c -o link_recv -luring -O3 -DUSE_LINK=0 > $ ./link_recv 12345 > $ cargo run --release # On another console > Benchmarking: 127.0.0.1:12345 > 50 clients, running 512 bytes, 60 sec. > > Speed: 168264 request/sec, 168264 response/sec > Requests: 10095846 > Responses: 10095844 > > $ gcc link_recv.c -o link_recv -luring -O3 -DUSE_LINK=1 > $ ./link_recv 12345 > $ cargo run --release # On another console > Benchmarking: 127.0.0.1:12345 > 50 clients, running 512 bytes, 60 sec. > > Speed: 112666 request/sec, 112666 response/sec > Requests: 6760009 > Responses: 6759975 > > > I think `POLL_ADD(POLLIN)-RECV` and `POLL_ADD(POLLOUT)-SEND` are common use cases for networking ( for some reason a short read for SEND is not considered an error, `RECV-SEND` cannot be used in a link chain ). RECV/SEND won't block after polled. I expect better performance for fewer io_uring_enter syscalls. Could you please have a check with it? > > Another more complex test case `POLL_ADD-READ_FIXED-WRITE_FIXED` I have posted on Github, which currently results in freeze. > > https://github.com/axboe/liburing/issues/71 > > Carter > > --- > > #include <stdio.h> > #include <stdlib.h> > #include <string.h> > #include <unistd.h> > > #include <sys/socket.h> > #include <sys/poll.h> > #include <netinet/in.h> > > #include <liburing.h> > > #define BACKLOG 128 > #define MAX_MESSAGE_LEN 1024 > #define MAX_CONNECTIONS 1024 > #ifndef USE_LINK > # define USE_LINK 0 > #endif > > enum { ACCEPT, POLL, READ, WRITE }; > > struct conn_info { > __u32 fd; > __u32 type; > }; > > typedef char buf_type[MAX_CONNECTIONS][MAX_MESSAGE_LEN]; > > static struct io_uring ring; > static unsigned cqe_count = 0; > > int init_socket(int portno) { > int sock_listen_fd = socket(AF_INET, SOCK_STREAM, 0); > if (sock_listen_fd < 0) { > perror("socket"); > return -1; > } > > struct sockaddr_in server_addr = { > .sin_family = AF_INET, > .sin_port = htons(portno), > .sin_addr = { > .s_addr = INADDR_ANY, > }, > }; > > if (bind(sock_listen_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) { > perror("bind"); > return -1; > } > > if (listen(sock_listen_fd, BACKLOG) < 0) { > perror("listen"); > return -1; > } > > return sock_listen_fd; > } > > static struct io_uring_sqe* get_sqe_safe() { > struct io_uring_sqe *sqe = io_uring_get_sqe(&ring); > if (__builtin_expect(!!sqe, 1)) { > return sqe; > } else { > io_uring_cq_advance(&ring, cqe_count); > cqe_count = 0; > io_uring_submit(&ring); > return io_uring_get_sqe(&ring); > } > } > > static void add_accept(int fd, struct sockaddr *client_addr, socklen_t *client_len) { > struct io_uring_sqe *sqe = get_sqe_safe(); > struct conn_info conn_i = { > .fd = fd, > .type = ACCEPT, > }; > > io_uring_prep_accept(sqe, fd, client_addr, client_len, 0); > memcpy(&sqe->user_data, &conn_i, sizeof(conn_i)); > } > > static void add_poll(int fd, int poll_mask, unsigned flags) { > struct io_uring_sqe *sqe = get_sqe_safe(); > struct conn_info conn_i = { > .fd = fd, > .type = POLL, > }; > > io_uring_prep_poll_add(sqe, fd, poll_mask); > io_uring_sqe_set_flags(sqe, flags); > memcpy(&sqe->user_data, &conn_i, sizeof(conn_i)); > } > > static void add_socket_read(int fd, size_t size, buf_type *bufs) { > struct io_uring_sqe *sqe = get_sqe_safe(); > struct conn_info conn_i = { > .fd = fd, > .type = READ, > }; > > io_uring_prep_recv(sqe, fd, (*bufs)[fd], size, MSG_NOSIGNAL); > memcpy(&sqe->user_data, &conn_i, sizeof(conn_i)); > } > > static void add_socket_write(int fd, size_t size, buf_type *bufs, unsigned flags) { > struct io_uring_sqe *sqe = get_sqe_safe(); > struct conn_info conn_i = { > .fd = fd, > .type = WRITE, > }; > > io_uring_prep_send(sqe, fd, (*bufs)[fd], size, MSG_NOSIGNAL); > io_uring_sqe_set_flags(sqe, flags); > memcpy(&sqe->user_data, &conn_i, sizeof(conn_i)); > } > > int main(int argc, char *argv[]) { > if (argc < 2) { > fprintf(stderr, "Please give a port number: %s [port]\n", argv[0]); > return 1; > } > > int portno = strtol(argv[1], NULL, 10); > int sock_listen_fd = init_socket(portno); > if (sock_listen_fd < 0) return -1; > printf("io_uring echo server listening for connections on port: %d\n", portno); > > > int ret = io_uring_queue_init(BACKLOG, &ring, 0); > if (ret < 0) { > fprintf(stderr, "queue_init: %s\n", strerror(-ret)); > return -1; > } > > buf_type *bufs = (buf_type *)malloc(sizeof(*bufs)); > > struct sockaddr_in client_addr; > socklen_t client_len = sizeof(client_addr); > add_accept(sock_listen_fd, (struct sockaddr *)&client_addr, &client_len); > > while (1) { > io_uring_submit_and_wait(&ring, 1); > > struct io_uring_cqe *cqe; > unsigned head; > > io_uring_for_each_cqe(&ring, head, cqe) { > ++cqe_count; > > struct conn_info conn_i; > memcpy(&conn_i, &cqe->user_data, sizeof(conn_i)); > int result = cqe->res; > > switch (conn_i.type) { > case ACCEPT: > #if USE_LINK > add_poll(result, POLLIN, IOSQE_IO_LINK); > add_socket_read(result, MAX_MESSAGE_LEN, bufs); > #else > add_poll(result, POLLIN, 0); > #endif > add_accept(sock_listen_fd, (struct sockaddr *)&client_addr, &client_len); > break; > > #if !USE_LINK > case POLL: > add_socket_read(conn_i.fd, MAX_MESSAGE_LEN, bufs); > break; > #endif > > case READ: > if (__builtin_expect(result <= 0, 0)) { > shutdown(conn_i.fd, SHUT_RDWR); > } else { > add_socket_write(conn_i.fd, result, bufs, 0); > } > break; > > case WRITE: > #if USE_LINK > add_poll(conn_i.fd, POLLIN, IOSQE_IO_LINK); > add_socket_read(conn_i.fd, MAX_MESSAGE_LEN, bufs); > #else > add_poll(conn_i.fd, POLLIN, 0); > #endif > break; > } > } > > io_uring_cq_advance(&ring, cqe_count); > cqe_count = 0; > } > > > close(sock_listen_fd); > free(bufs); > } > > > >> 2020年2月13日 上午1:11，Jens Axboe <axboe@xxxxxxxxx> 写道： >> >> On 2/12/20 9:31 AM, Carter Li 李通洲 wrote: >>> Hi everyone, >>> >>> IOSQE_IO_LINK seems to have very high cost, even greater then io_uring_enter syscall. >>> >>> Test code attached below. The program completes after getting 100000000 cqes. >>> >>> $ gcc test.c -luring -o test0 -g -O3 -DUSE_LINK=0 >>> $ time ./test0 >>> USE_LINK: 0, count: 100000000, submit_count: 1562500 >>> 0.99user 9.99system 0:11.02elapsed 99%CPU (0avgtext+0avgdata 1608maxresident)k >>> 0inputs+0outputs (0major+72minor)pagefaults 0swaps >>> >>> $ gcc test.c -luring -o test1 -g -O3 -DUSE_LINK=1 >>> $ time ./test1 >>> USE_LINK: 1, count: 100000110, submit_count: 799584 >>> 0.83user 19.21system 0:20.90elapsed 95%CPU (0avgtext+0avgdata 1632maxresident)k >>> 0inputs+0outputs (0major+72minor)pagefaults 0swaps >>> >>> As you can see, the `-DUSE_LINK=1` version emits only about half io_uring_submit calls >>> of the other version, but takes twice as long. That makes IOSQE_IO_LINK almost useless, >>> please have a check. >> >> The nop isn't really a good test case, as it doesn't contain any smarts >> in terms of executing a link fast. So it doesn't say a whole lot outside >> of "we could make nop links faster", which is also kind of pointless. >> >> "Normal" commands will work better. Where the link is really a win is if >> the first request needs to go async to complete. For that case, the >> next link can execute directly from that context. This saves an async >> punt for the common case. >> >> -- >> Jens Axboe >> > -- Pavel Begunkov
