sorry i accidentally pressed send message... run out of SQE should not be problem, when io_uring_get_sqe(https://github.com/axboe/liburing/blob/master/src/queue.c#L409) returns a null, you can run io_uring_submit in netty we do that automatically when its full https://github.com/netty/netty-incubator-transport-io_uring/blob/main/transport-classes-io_uring/src/main/java/io/netty/incubator/channel/uring/IOUringSubmissionQueue.java#L117 In theory you could run out of CQE, netty io_uring approach is a little bit different. https://github.com/netty/netty-incubator-transport-io_uring/blob/main/transport-classes-io_uring/src/main/java/io/netty/incubator/channel/uring/IOUringCompletionQueue.java#L86 (similar to io_uring_for_each_cqe) to make sure the kernel sees that and the process function is called here https://github.com/netty/netty-incubator-transport-io_uring/blob/main/transport-classes-io_uring/src/main/java/io/netty/incubator/channel/uring/IOUringEventLoop.java#L203 > On Wed, 12 Jan 2022 at 22:17, dormando <dormando@xxxxxxxxx> wrote: > > > > Hey, > > > > Been integrating io_uring in my stack which has been going well-ish. > > Wondering if you folks have seen implementations of client libraries that > > feel clean and user friendly? > > > > IE: with poll/select/epoll/kqueue most client libraries (like libcurl) > > implement functions like "client_send_data(ctx, etc)", which returns > > -WANT_READ/-WANT_WRITE/etc and an fd if it needs more data to move > > forward. With the syscalls themselves externalized in io_uring I'm > > struggling to come up with abstractions I like and haven't found much > > public on a googlin'. Do any public ones exist yet? > > > > On implementing networked servers, it feels natural to do a core loop > > like: > > > > while (1) { > > io_uring_submit_and_wait(&t->ring, 1); > > > > uint32_t head = 0; > > uint32_t count = 0; > > > > io_uring_for_each_cqe(&t->ring, head, cqe) { > > > > event *pe = io_uring_cqe_get_data(cqe); > > pe->callback(pe->udata, cqe); > > > > count++; > > } > > io_uring_cq_advance(&t->ring, count); > > } > > > > ... but A) you can run out of SQE's if they're generated from within > > callbacks()'s (retries, get further data, writes after reads, etc). > > B) Run out of CQE's with IORING_FEAT_NODROP and can no longer free up > > SQE's > > > > So this loop doesn't work under pressure :) > > > > I see that qemu's implementation walks an object queue, which calls > > io_uring_submit() if SQE's are exhausted. I don't recall it trying to do > > anything if submit returns EBUSY because of CQE exhaustion? I've not found > > other merged code implementing non-toy network servers and most examples > > are rewrites of CLI tooling which are much more constrained problems. Have > > I missed anything? > > > > I can make this work but a lot of solutions are double walking lists > > (fetch all CQE's into an array, advance them, then process), or not being > > able to take advantage of any of the batching API's. Hoping the > > community's got some better examples to untwist my brain a bit :) > > > > For now I have things working but want to do a cleanup pass before making > > my clients/server bits public facing. > > > > Thanks! > > -Dormando > > > > -- > Josef Grieb -- Josef Grieb
