Oliver Crumrine wrote: > Pavel Begunkov wrote: > > On 4/5/24 21:04, Oliver Crumrine wrote: > > > Pavel Begunkov wrote: > > >> On 4/4/24 23:17, Oliver Crumrine wrote: > > >>> In his patch to enable zerocopy networking for io_uring, Pavel Begunkov > > >>> specifically disabled REQ_F_CQE_SKIP, as (at least from my > > >>> understanding) the userspace program wouldn't receive the > > >>> IORING_CQE_F_MORE flag in the result value. > > >> > > >> No. IORING_CQE_F_MORE means there will be another CQE from this > > >> request, so a single CQE without IORING_CQE_F_MORE is trivially > > >> fine. > > >> > > >> The problem is the semantics, because by suppressing the first > > >> CQE you're loosing the result value. You might rely on WAITALL > > > That's already happening with io_send. > > > > Right, and it's still annoying and hard to use > Another solution might be something where there is a counter that stores > how many CQEs with REQ_F_CQE_SKIP have been processed. Before exiting, > userspace could call a function like: io_wait_completions(int completions) > which would wait until everything is done, and then userspace could peek > the completion ring. > > > > >> as other sends and "fail" (in terms of io_uring) the request > > >> in case of a partial send posting 2 CQEs, but that's not a great > > >> way and it's getting userspace complicated pretty easily. > > >> > > >> In short, it was left out for later because there is a > > >> better way to implement it, but it should be done carefully > > > Maybe we could put the return values in the notifs? That would be a > > > discrepancy between io_send and io_send_zc, though. > > > > Yes. And yes, having a custom flavour is not good. It'd only > > be well usable if apart from returning the actual result > > it also guarantees there will be one and only one CQE, then > > the userspace doesn't have to do the dancing with counting > > and checking F_MORE. In fact, I outlined before how a generic > > solution may looks like: > > > > https://github.com/axboe/liburing/issues/824 > > > > The only interesting part, IMHO, is to be able to merge the > > main completion with its notification. Below is an old stash > > rebased onto for-6.10. The only thing missing is relinking, > > but maybe we don't even care about it. I need to cover it > > well with tests. > The patch looks pretty good. The only potential issue is that you store > the res of the normal CQE into the notif CQE. This overwrites the > IORING_CQE_F_NOTIF with IORING_CQE_F_MORE. This means that the notif would > indicate to userspace that there will be another CQE, of which there > won't. I was wrong here; Mixed up flags and result value. > > > > > > > > > > commit ca5e4fb6d105b5dfdf3768d46ce01529b7bb88c5 > > Author: Pavel Begunkov <asml.silence@xxxxxxxxx> > > Date: Sat Apr 6 15:46:38 2024 +0100 > > > > io_uring/net: introduce single CQE send zc mode > > > > IORING_OP_SEND[MSG]_ZC requests are posting two completions, one to > > notify that the data was queued, and later a second, usually referred > > as "notification", to let the user know that the buffer used can be > > reused/freed. In some cases the user might not care about the main > > completion and would be content getting only the notification, which > > would allow to simplify the userspace. > > > > One example is when after a send the user would be waiting for the other > > end to get the message and reply back not pushing any more data in the > > meantime. Another case is unreliable protocols like UDP, which do not > > require a confirmation from the other end before dropping buffers, and > > so the notifications are usually posted shortly after the send request > > is queued. > > > > Add a flag merging completions into a single CQE. cqe->res will store > > the send's result as usual, and it will have IORING_CQE_F_NOTIF set if > > the buffer was potentially used. Timewise, it would be posted at the > > moment when the notification would have been originally completed. > > > > Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx> > > > > diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h > > index 7bd10201a02b..e2b528c341c9 100644 > > --- a/include/uapi/linux/io_uring.h > > +++ b/include/uapi/linux/io_uring.h > > @@ -356,6 +356,7 @@ enum io_uring_op { > > #define IORING_RECV_MULTISHOT (1U << 1) > > #define IORING_RECVSEND_FIXED_BUF (1U << 2) > > #define IORING_SEND_ZC_REPORT_USAGE (1U << 3) > > +#define IORING_SEND_ZC_COMBINE_CQE (1U << 4) > > > > /* > > * cqe.res for IORING_CQE_F_NOTIF if > > diff --git a/io_uring/net.c b/io_uring/net.c > > index a74287692071..052f030ab8f8 100644 > > --- a/io_uring/net.c > > +++ b/io_uring/net.c > > @@ -992,7 +992,19 @@ void io_send_zc_cleanup(struct io_kiocb *req) > > } > > } > > > > -#define IO_ZC_FLAGS_COMMON (IORING_RECVSEND_POLL_FIRST | IORING_RECVSEND_FIXED_BUF) > > +static inline void io_sendzc_adjust_res(struct io_kiocb *req) > > +{ > > + struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg); > > + > > + if (sr->flags & IORING_SEND_ZC_COMBINE_CQE) { > > + sr->notif->cqe.res = req->cqe.res; > > + req->flags |= REQ_F_CQE_SKIP; > > + } > > +} > > + > > +#define IO_ZC_FLAGS_COMMON (IORING_RECVSEND_POLL_FIRST | \ > > + IORING_RECVSEND_FIXED_BUF | \ > > + IORING_SEND_ZC_COMBINE_CQE) > > #define IO_ZC_FLAGS_VALID (IO_ZC_FLAGS_COMMON | IORING_SEND_ZC_REPORT_USAGE) > > > > int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) > > @@ -1022,6 +1034,8 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) > > if (zc->flags & ~IO_ZC_FLAGS_VALID) > > return -EINVAL; > > if (zc->flags & IORING_SEND_ZC_REPORT_USAGE) { > > + if (zc->flags & IORING_SEND_ZC_COMBINE_CQE) > > + return -EINVAL; > > io_notif_set_extended(notif); > > io_notif_to_data(notif)->zc_report = true; > > } > > @@ -1197,6 +1211,9 @@ int io_send_zc(struct io_kiocb *req, unsigned int issue_flags) > > else if (zc->done_io) > > ret = zc->done_io; > > > > + io_req_set_res(req, ret, IORING_CQE_F_MORE); > > + io_sendzc_adjust_res(req); > > + > > /* > > * If we're in io-wq we can't rely on tw ordering guarantees, defer > > * flushing notif to io_send_zc_cleanup() > > @@ -1205,7 +1222,6 @@ int io_send_zc(struct io_kiocb *req, unsigned int issue_flags) > > io_notif_flush(zc->notif); > > io_req_msg_cleanup(req, 0); > > } > > - io_req_set_res(req, ret, IORING_CQE_F_MORE); > > return IOU_OK; > > } > > > > > else if (sr->done_io) > > ret = sr->done_io; > > > > + io_req_set_res(req, ret, IORING_CQE_F_MORE); > > + io_sendzc_adjust_res(req); > > + > > /* > > * If we're in io-wq we can't rely on tw ordering guarantees, defer > > * flushing notif to io_send_zc_cleanup() > > @@ -1266,7 +1285,6 @@ int io_sendmsg_zc(struct io_kiocb *req, unsigned int issue_flags) > > io_notif_flush(sr->notif); > > io_req_msg_cleanup(req, 0); > > } > > - io_req_set_res(req, ret, IORING_CQE_F_MORE); > > return IOU_OK; > > } > > > > @@ -1278,8 +1296,10 @@ void io_sendrecv_fail(struct io_kiocb *req) > > req->cqe.res = sr->done_io; > > > > if ((req->flags & REQ_F_NEED_CLEANUP) && > > - (req->opcode == IORING_OP_SEND_ZC || req->opcode == IORING_OP_SENDMSG_ZC)) > > + (req->opcode == IORING_OP_SEND_ZC || req->opcode == IORING_OP_SENDMSG_ZC)) { > > req->cqe.flags |= IORING_CQE_F_MORE; > > + io_sendzc_adjust_res(req); > > + } > > } > > > > int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) > > > > > > -- > > Pavel Begunkov > >
