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. 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 >
