From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f44.google.com (mail-wm1-f44.google.com [209.85.128.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C20091353E3; Sun, 7 Apr 2024 13:13:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.44 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712495639; cv=none; b=MNujIyF7GCsuykBmDWxDLlkcFDkOXydpSY9YcRK6yD2JGDz/4R9XqvQ6k/05fnqDuP57KIUJkYEnHwdBqL9S/xBJN1Adt0cGHhM5AkiG8KfpASmHi1jT2E+0SBUIDKgn7D/NXXPdjRAsxgNY+218/jaycAAbV9RrJvTWXIMgpOI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712495639; c=relaxed/simple; bh=yzaslZjG9r8gxOy7pz+qgUzY/Om3cUHp6ppl1M1nP94=; h=From:In-Reply-To:References:Mime-Version:Date:Message-ID:Subject: To:Cc:Content-Type; b=DFc3HwM9W2YI2mbX/aTK4hg4BtWhx7P5MGVIZavouH2o1a5WmzsJ9qF5lDOuks3H1s706s4fL5hr4sVsDeWdjqSL94VOdBcQJeo9JE31zL7JGQzVrEIvmARCw73fjHZES/FpPN6K4Po/sZMctlapXCi39TzRI8foPoI5OfVZ2TU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=I1kuqwhZ; arc=none smtp.client-ip=209.85.128.44 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="I1kuqwhZ" Received: by mail-wm1-f44.google.com with SMTP id 5b1f17b1804b1-4164c9debf6so3409805e9.1; Sun, 07 Apr 2024 06:13:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1712495636; x=1713100436; darn=vger.kernel.org; h=cc:to:subject:message-id:date:mime-version:references:in-reply-to :from:from:to:cc:subject:date:message-id:reply-to; bh=7zi9maRkKEe1wJTBLEw6CNhNtu7l7A3MQCK2xzWXoig=; b=I1kuqwhZpJ2nn4dCZRaCerfj3NkH87kfUpMjNHvC9qNnga0jogrzg4j9H+pGlfom+6 86AstJjHM77z7v844rwAuwA7VTc47MGC3gRAKvt2T6EeBJ9KneE3ZxPEHDKxD/pU2ytk dq1sVlTDUL6kSAUrCmb2oQPsuN1JMeLwTvSM3gd11h5VlGAWldgo26aXrpew6/LrrD4T KyYLWPjZP4yO2BmxyGFhSaCkuuNuhk0C0PxCWjaRI1RxtjQLuhLErWp1qO+dkuLJeJFr p54lqsEoy9y5udlIm30STl6CA6Bf6hpwVUih7dpD43PCbKcJnOXX87OK2dabnsl41RPM s5kQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1712495636; x=1713100436; h=cc:to:subject:message-id:date:mime-version:references:in-reply-to :from:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=7zi9maRkKEe1wJTBLEw6CNhNtu7l7A3MQCK2xzWXoig=; b=tf689o5PgrVoAETLZr9LvZhXVz6wgCxPg/F1wxgpHYzfLm/zbHcUKheROx4vgSi9ph h1bHbb635+uujCONxYgmXCuXT20/0g36EcYgzlNuaRpOhlLnbyXQEvULe1cukJgk3m2Y wq3A5Xn6MYQYxNBJ2cQ8lrPkBjCvCx7ksvHFnUb9dadpzyBNVVQb70uuo3gpjlHkjxUz 1vrYGA33oQ0udXPiGkonakkqX41Z7sVvN8m4fB5XI7N38ls1Dgr26Gi3gIHuS2kQpLbw DGJ/GXaThUJXggjt9rU8Fa4hhP5b3nuhwdqe0RRS8OJwJpb2xit2clN9fJ5SVU2BGJNv LCYg== X-Forwarded-Encrypted: i=1; AJvYcCVF+gzreK5LCv7A/cyLu+HZ3AWN3Ou47JZ6eUGbwD/O5fJ+YlpBViq123ywcZ53ZqbttkCbI1swaP/eHq1zRyLSW/WH/onI9YUPvw5q X-Gm-Message-State: AOJu0YyVQp3+U15zM8NpysZFS7opYoEB+2CjjIOkzRr64hkbUkRA0gbb vAzGXMBcWpmrKW+0/mo/hJQFkQSyGxIG+cPCYjNDaDNvK+fl9/7floxY6dnnl51L792vq2W1/o+ E1GTa+0mrL8hYUeIpSrBtpKZzBeE= X-Google-Smtp-Source: AGHT+IFMQd5Z4mba0t8DcKyItcYtNm+DHIZknZxgWv30j3wm1Ztc+J3cCnVxY4y1XMGUMvivR3rrYW8ZPFfLWyOulmM= X-Received: by 2002:a5d:5708:0:b0:343:3538:4ee4 with SMTP id a8-20020a5d5708000000b0034335384ee4mr3582507wrv.45.1712495635860; Sun, 07 Apr 2024 06:13:55 -0700 (PDT) Received: from 753933720722 named unknown by gmailapi.google.com with HTTPREST; Sun, 7 Apr 2024 06:13:55 -0700 From: Oliver Crumrine In-Reply-To: References: <6850f08d-0e89-4eb3-bbfb-bdcc5d4e1b78@gmail.com> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Date: Sun, 7 Apr 2024 06:13:55 -0700 Message-ID: Subject: Re: [PATCH 1/3] io_uring: Add REQ_F_CQE_SKIP support for io_uring zerocopy To: Pavel Begunkov , Oliver Crumrine , axboe@kernel.dk Cc: io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" 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. > > > > > commit ca5e4fb6d105b5dfdf3768d46ce01529b7bb88c5 > Author: Pavel Begunkov > 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 > > 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