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Tue, 17 Dec 2019 10:01:19 -0800 (PST) Subject: Re: [PATCH 3/3] io_uring: move *queue_link_head() from common path To: Pavel Begunkov , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <17f7900c-385f-0dfa-11bf-af99d080f894@gmail.com> <76917820-052d-9597-133d-424fee3edade@kernel.dk> <5d4af2f6-26a2-b241-5131-3a0155cbbf22@kernel.dk> <3b5100a7-2922-a9f2-e4e2-76252318959d@gmail.com> From: Jens Axboe Message-ID: <7edd6631-326c-ac9c-7c5b-fa4bab3932d3@kernel.dk> Date: Tue, 17 Dec 2019 11:01:18 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <3b5100a7-2922-a9f2-e4e2-76252318959d@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 12/17/19 10:52 AM, Pavel Begunkov wrote: > On 17/12/2019 20:37, Jens Axboe wrote: >> On 12/17/19 9:45 AM, Jens Axboe wrote: >>> On 12/16/19 4:38 PM, Pavel Begunkov wrote: >>>> On 17/12/2019 02:22, Pavel Begunkov wrote: >>>>> Move io_queue_link_head() to links handling code in io_submit_sqe(), >>>>> so it wouldn't need extra checks and would have better data locality. >>>>> >>>>> Signed-off-by: Pavel Begunkov >>>>> --- >>>>> fs/io_uring.c | 32 ++++++++++++++------------------ >>>>> 1 file changed, 14 insertions(+), 18 deletions(-) >>>>> >>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>>> index bac9e711e38d..a880ed1409cb 100644 >>>>> --- a/fs/io_uring.c >>>>> +++ b/fs/io_uring.c >>>>> @@ -3373,13 +3373,15 @@ static bool io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state, >>>>> struct io_kiocb **link) >>>>> { >>>>> struct io_ring_ctx *ctx = req->ctx; >>>>> + unsigned int sqe_flags; >>>>> int ret; >>>>> >>>>> + sqe_flags = READ_ONCE(req->sqe->flags); >>>>> req->user_data = READ_ONCE(req->sqe->user_data); >>>>> trace_io_uring_submit_sqe(ctx, req->user_data, true, req->in_async); >>>>> >>>>> /* enforce forwards compatibility on users */ >>>>> - if (unlikely(req->sqe->flags & ~SQE_VALID_FLAGS)) { >>>>> + if (unlikely(sqe_flags & ~SQE_VALID_FLAGS)) { >>>>> ret = -EINVAL; >>>>> goto err_req; >>>>> } >>>>> @@ -3402,10 +3404,10 @@ static bool io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state, >>>>> if (*link) { >>>>> struct io_kiocb *head = *link; >>>>> >>>>> - if (req->sqe->flags & IOSQE_IO_DRAIN) >>>>> + if (sqe_flags & IOSQE_IO_DRAIN) >>>>> head->flags |= REQ_F_DRAIN_LINK | REQ_F_IO_DRAIN; >>>>> >>>>> - if (req->sqe->flags & IOSQE_IO_HARDLINK) >>>>> + if (sqe_flags & IOSQE_IO_HARDLINK) >>>>> req->flags |= REQ_F_HARDLINK; >>>>> >>>>> if (io_alloc_async_ctx(req)) { >>>>> @@ -3421,9 +3423,15 @@ static bool io_submit_sqe(struct io_kiocb *req, struct io_submit_state *state, >>>>> } >>>>> trace_io_uring_link(ctx, req, head); >>>>> list_add_tail(&req->link_list, &head->link_list); >>>>> - } else if (req->sqe->flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) { >>>>> + >>>>> + /* last request of a link, enqueue the link */ >>>>> + if (!(sqe_flags & IOSQE_IO_LINK)) { >>>> >>>> This looks suspicious (as well as in the current revision). Returning back >>>> to my questions a few days ago can sqe->flags have IOSQE_IO_HARDLINK, but not >>>> IOSQE_IO_LINK? I don't find any check. >>>> >>>> In other words, should it be as follows? >>>> !(sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) >>> >>> Yeah, I think that should check for both. I'm fine with either approach >>> in general: >>> >>> - IOSQE_IO_HARDLINK must have IOSQE_IO_LINK set >>> >>> or >>> >>> - IOSQE_IO_HARDLINK implies IOSQE_IO_LINK >>> >>> Seems like the former is easier to verify in terms of functionality, >>> since we can rest easy if we check this early and -EINVAL if that isn't >>> the case. >>> >>> What do you think? >> >> If you agree, want to send in a patch for that for 5.5? Then I can respin >> for-5.6/io_uring on top of that, and we can apply your cleanups there. >> > Yes, that's the idea. Already got a patch, if you haven't done it yet. I haven't. > Just was thinking, whether to add a check for not setting both flags > at the same moment in the "imply" case. Would give us 1 state in 2 bits > for future use. Not sure I follow what you're saying here, can you elaborate? -- Jens Axboe