On 9/3/21 12:00 PM, Hao Xu wrote:
> Refactor io_accept() to support multishot mode.
Multishot with the fixed/direct mode sounds weird (considering that
the slot index is specified by userspace), let's forbid them.
io_accept_prep() {
if (accept->file_slot && (flags & MULTISHOT))
return -EINVAL;
...
}
> theoretical analysis:
> 1) when connections come in fast
> - singleshot:
> add accept sqe(userpsace) --> accept inline
> ^ |
> |-----------------|
> - multishot:
> add accept sqe(userspace) --> accept inline
> ^ |
> |--*--|
>
> we do accept repeatedly in * place until get EAGAIN
>
> 2) when connections come in at a low pressure
> similar thing like 1), we reduce a lot of userspace-kernel context
> switch and useless vfs_poll()
>
> tests:
> Did some tests, which goes in this way:
>
> server client(multiple)
> accept connect
> read write
> write read
> close close
>
> Basically, raise up a number of clients(on same machine with server) to
> connect to the server, and then write some data to it, the server will
> write those data back to the client after it receives them, and then
> close the connection after write return. Then the client will read the
> data and then close the connection. Here I test 10000 clients connect
> one server, data size 128 bytes. And each client has a go routine for
> it, so they come to the server in short time.
> test 20 times before/after this patchset, time spent:(unit cycle, which
> is the return value of clock())
> before:
> 1930136+1940725+1907981+1947601+1923812+1928226+1911087+1905897+1941075
> +1934374+1906614+1912504+1949110+1908790+1909951+1941672+1969525+1934984
> +1934226+1914385)/20.0 = 1927633.75
> after:
> 1858905+1917104+1895455+1963963+1892706+1889208+1874175+1904753+1874112
> +1874985+1882706+1884642+1864694+1906508+1916150+1924250+1869060+1889506
> +1871324+1940803)/20.0 = 1894750.45
>
> (1927633.75 - 1894750.45) / 1927633.75 = 1.65%
>
> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
> ---
>
> not sure if we should cancel it when io_cqring_fill_event() reurn false
>
> fs/io_uring.c | 34 +++++++++++++++++++++++++++++-----
> 1 file changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index dae7044e0c24..eb81d37dce78 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -4885,16 +4885,18 @@ static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>
> static int io_accept(struct io_kiocb *req, unsigned int issue_flags)
> {
> + struct io_ring_ctx *ctx = req->ctx;
> struct io_accept *accept = &req->accept;
> bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
> unsigned int file_flags = force_nonblock ? O_NONBLOCK : 0;
> bool fixed = !!accept->file_slot;
> struct file *file;
> - int ret, fd;
> + int ret, ret2 = 0, fd;
>
> if (req->file->f_flags & O_NONBLOCK)
> req->flags |= REQ_F_NOWAIT;
>
> +retry:
> if (!fixed) {
> fd = __get_unused_fd_flags(accept->flags, accept->nofile);
> if (unlikely(fd < 0))
> @@ -4906,20 +4908,42 @@ static int io_accept(struct io_kiocb *req, unsigned int issue_flags)
> if (!fixed)
> put_unused_fd(fd);
> ret = PTR_ERR(file);
> - if (ret == -EAGAIN && force_nonblock)
> - return -EAGAIN;
> + if (ret == -EAGAIN && force_nonblock) {
> + if ((req->flags & (REQ_F_APOLL_MULTISHOT | REQ_F_POLLED)) ==
> + (REQ_F_APOLL_MULTISHOT | REQ_F_POLLED))
> + ret = 0;
> + return ret;
> + }
> if (ret == -ERESTARTSYS)
> ret = -EINTR;
> req_set_fail(req);
> } else if (!fixed) {
> fd_install(fd, file);
> ret = fd;
> + /*
> + * if it's in multishot mode, let's return -EAGAIN to make it go
> + * into fast poll path
> + */
> + if ((req->flags & REQ_F_APOLL_MULTISHOT) && force_nonblock &&
> + !(req->flags & REQ_F_POLLED))
> + ret2 = -EAGAIN;
> } else {
> ret = io_install_fixed_file(req, file, issue_flags,
> accept->file_slot - 1);
> }
> - __io_req_complete(req, issue_flags, ret, 0);
> - return 0;
> +
> + if (req->flags & REQ_F_APOLL_MULTISHOT) {
> + spin_lock(&ctx->completion_lock);
> + if (io_cqring_fill_event(ctx, req->user_data, ret, 0)) {
> + io_commit_cqring(ctx);
> + ctx->cq_extra++;
> + }
> + spin_unlock(&ctx->completion_lock);
> + goto retry;
> + } else {
> + __io_req_complete(req, issue_flags, ret, 0);
> + }
> + return ret2;
> }
>
> static int io_connect_prep_async(struct io_kiocb *req)
>
--
Pavel Begunkov
