On 5/4/22 9:28 AM, Jens Axboe wrote: > On 5/4/22 9:21 AM, Constantine Gavrilov wrote: >> On Wed, May 4, 2022 at 4:54 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >>> >>> On 5/3/22 5:05 PM, Constantine Gavrilov wrote: >>>> Jens: >>>> >>>> This is related to the previous thread "Fix MSG_WAITALL for >>>> IORING_OP_RECV/RECVMSG". >>>> >>>> We have a similar issue with TCP socket sends. I see short sends >>>> regarding of the method (I tried write, writev, send, and sendmsg >>>> opcodes, while using MSG_WAITALL for send and sendmsg). It does not >>>> make a difference. >>>> >>>> Most of the time, sends are not short, and I never saw short sends >>>> with loopback and my app. But on real network media, I see short >>>> sends. >>>> >>>> This is a real problem, since because of this it is not possible to >>>> implement queue size of > 1 on a TCP socket, which limits the benefit >>>> of IORING. When we have a short send, the next send in queue will >>>> "corrupt" the stream. >>>> >>>> Can we have complete send before it completes, unless the socket is >>>> disconnected? >>> >>> I'm guessing that this happens because we get a task_work item queued >>> after we've processed some of the send, but not all. What kernel are you >>> using? >>> >>> This: >>> >>> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.19/io_uring&id=4c3c09439c08b03d9503df0ca4c7619c5842892e >>> >>> is queued up for 5.19, would be worth trying. >>> >>> -- >>> Jens Axboe >>> >> >> Jens: >> >> Thank you for your reply. >> >> The kernel is 5.17.4-200.fc35.x86_64. I have looked at the patch. With >> the solution in place, I am wondering whether it will be possible to >> use multiple uring send IOs on the same socket. I expect that Linux >> TCP will serialize multiple send operations on the same socket. I am >> not sure it happens with uring (meaning that socket is blocked for >> processing a new IO until the pending IO completes). Do I need >> IOSQE_IO_DRAIN / IOSQE_IO_LINK for this to work? Would not be optimal >> because of multiple different sockets in the same uring. While I >> already have a workaround in the form of a "software" queue for >> streaming data on TCP sockets, I would rather have kernel to do >> "native" queueing in sockets layer, and have exrtra CPU cycles >> available to the application. > > The patch above will mess with ordering potentially. If the cause is as > I suspect, task_work causing it to think it's signaled, then the better > approach may indeed be to just flush that work and retry without > re-queueing the current one. I can try a patch against 5.18 if you are > willing and able to test? You can try something like this, if you run my for-5.19/io_uring branch. I'd be curious to know if this solves the short send issue for you. diff --git a/fs/io_uring.c b/fs/io_uring.c index f6b6db216478..b835e80be1fa 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -5684,6 +5684,7 @@ static int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags) if (flags & MSG_WAITALL) min_ret = iov_iter_count(&kmsg->msg.msg_iter); +retry: ret = __sys_sendmsg_sock(sock, &kmsg->msg, flags); if (ret < min_ret) { @@ -5694,6 +5695,8 @@ static int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags) if (ret > 0 && io_net_retry(sock, flags)) { sr->done_io += ret; req->flags |= REQ_F_PARTIAL_IO; + if (io_run_task_work()) + goto retry; return io_setup_async_msg(req, kmsg); } req_set_fail(req); @@ -5744,6 +5747,7 @@ static int io_send(struct io_kiocb *req, unsigned int issue_flags) min_ret = iov_iter_count(&msg.msg_iter); msg.msg_flags = flags; +retry: ret = sock_sendmsg(sock, &msg); if (ret < min_ret) { if (ret == -EAGAIN && (issue_flags & IO_URING_F_NONBLOCK)) @@ -5755,6 +5759,8 @@ static int io_send(struct io_kiocb *req, unsigned int issue_flags) sr->buf += ret; sr->done_io += ret; req->flags |= REQ_F_PARTIAL_IO; + if (io_run_task_work()) + goto retry; return -EAGAIN; } req_set_fail(req); -- Jens Axboe
