On Fri, 14 Jan 2022, Josef wrote: > 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 Thanks! Unless I'm completely misreading the liburing code, io_uring_submit() can return EBUSY and fail to submit the sqe's, if there is currently a queue of CQE's beyond the limit (ie; FEAT_NODROP). Which would mean you can't reliably submit when get_sqe() returns NULL? I hope I have this wrong since it would be much simpler otherwise :) > 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 Thanks. I'll study these a bit more. > > > > 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 >
