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Sat, 04 Sep 2021 15:41:32 -0700 (PDT) Subject: Re: [PATCH 5/6] io_uring: implement multishot mode for accept From: Pavel Begunkov To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-6-haoxu@linux.alibaba.com> <3070a597-3326-5cac-253e-e2b58eebd3a2@gmail.com> Message-ID: <64734f7c-aaee-7ac7-752e-2d81a475d3d8@gmail.com> Date: Sat, 4 Sep 2021 23:40:59 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <3070a597-3326-5cac-253e-e2b58eebd3a2@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/4/21 11:39 PM, Pavel Begunkov wrote: > 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; > ... > } Ah, never mind, it's already there in 6/6 > >> 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 >> --- >> >> 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