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SubjectRe: [PATCH 3/3] io_uring: move *queue_link_head() from common path
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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 <asml.silence@gmail.com>
> ---
> 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))

> + io_queue_link_head(head);
> + *link = NULL;
> + }
> + } else if (sqe_flags & (IOSQE_IO_LINK|IOSQE_IO_HARDLINK)) {
> req->flags |= REQ_F_LINK;
> - if (req->sqe->flags & IOSQE_IO_HARDLINK)
> + if (sqe_flags & IOSQE_IO_HARDLINK)
> req->flags |= REQ_F_HARDLINK;
>
> INIT_LIST_HEAD(&req->link_list);
> @@ -3540,10 +3548,8 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
> }
>
> for (i = 0; i < nr; i++) {
> - struct io_kiocb *req;
> - unsigned int sqe_flags;
> + struct io_kiocb *req = io_get_req(ctx, statep);
>
> - req = io_get_req(ctx, statep);
> if (unlikely(!req)) {
> if (!submitted)
> submitted = -EAGAIN;
> @@ -3563,8 +3569,6 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
> }
>
> submitted++;
> - sqe_flags = req->sqe->flags;
> -
> req->ring_file = ring_file;
> req->ring_fd = ring_fd;
> req->has_user = *mm != NULL;
> @@ -3572,14 +3576,6 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
> req->needs_fixed_file = async;
> if (!io_submit_sqe(req, statep, &link))
> break;
> - /*
> - * If previous wasn't linked and we have a linked command,
> - * that's the end of the chain. Submit the previous link.
> - */
> - if (!(sqe_flags & IOSQE_IO_LINK) && link) {
> - io_queue_link_head(link);
> - link = NULL;
> - }
> }
>
> if (link)
>

--
Pavel Begunkov

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