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. -- ---------------------------------------- Constantine Gavrilov Storage Architect Master Inventor Tel-Aviv IBM Storage Lab 1 Azrieli Center, Tel-Aviv ----------------------------------------
