Re: [ISSUE] The time cost of IOSQE_IO_LINK

["Carter Li 李通洲" <carter.li@eoitek.com>]

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@kernel.dk> 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
>