On 6/20/21 8:05 PM, Olivier Langlois wrote:
> It is quite frequent that when an operation fails and returns EAGAIN,
> the data becomes available between that failure and the call to
> vfs_poll() done by io_arm_poll_handler().
>
> Detecting the situation and reissuing the operation is much faster
> than going ahead and push the operation to the io-wq.
>
> Signed-off-by: Olivier Langlois <olivier@xxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 26 +++++++++++++++++---------
> 1 file changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index fa8794c61af7..6e037304429a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -5143,7 +5143,10 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
> return mask;
> }
>
> -static bool io_arm_poll_handler(struct io_kiocb *req)
> +#define IO_ARM_POLL_OK 0
> +#define IO_ARM_POLL_ERR 1
> +#define IO_ARM_POLL_READY 2
Please add a new line here. Can even be moved somewhere
to the top, but it's a matter of taste.
Also, how about to rename it to apoll? io_uring internal
rw/send/recv polling is often abbreviated as such around
io_uring.c
IO_APOLL_OK and so on.
> +static int io_arm_poll_handler(struct io_kiocb *req)
> {
> const struct io_op_def *def = &io_op_defs[req->opcode];
> struct io_ring_ctx *ctx = req->ctx;
> @@ -5153,22 +5156,22 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
> int rw;
>
> if (!req->file || !file_can_poll(req->file))
> - return false;
> + return IO_ARM_POLL_ERR;
It's not really an error. Maybe IO_APOLL_ABORTED or so?
> if (req->flags & REQ_F_POLLED)
> - return false;
> + return IO_ARM_POLL_ERR;
> if (def->pollin)
> rw = READ;
> else if (def->pollout)
> rw = WRITE;
> else
> - return false;
> + return IO_ARM_POLL_ERR;
> /* if we can't nonblock try, then no point in arming a poll handler */
> if (!io_file_supports_async(req, rw))
> - return false;
> + return IO_ARM_POLL_ERR;
>
> apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
> if (unlikely(!apoll))
> - return false;
> + return IO_ARM_POLL_ERR;
> apoll->double_poll = NULL;
>
> req->flags |= REQ_F_POLLED;
> @@ -5194,12 +5197,12 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
> if (ret || ipt.error) {
> io_poll_remove_double(req);
> spin_unlock_irq(&ctx->completion_lock);
> - return false;
> + return ret?IO_ARM_POLL_READY:IO_ARM_POLL_ERR;
spaces would be great.
> }
> spin_unlock_irq(&ctx->completion_lock);
> trace_io_uring_poll_arm(ctx, req->opcode, req->user_data, mask,
> apoll->poll.events);
> - return true;
> + return IO_ARM_POLL_OK;
> }
>
> static bool __io_poll_remove_one(struct io_kiocb *req,
> @@ -6416,6 +6419,7 @@ static void __io_queue_sqe(struct io_kiocb *req)
> struct io_kiocb *linked_timeout = io_prep_linked_timeout(req);
> int ret;
>
> +issue_sqe:
> ret = io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_COMPLETE_DEFER);
>
> /*
> @@ -6435,12 +6439,16 @@ static void __io_queue_sqe(struct io_kiocb *req)
> io_put_req(req);
> }
> } else if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) {
> - if (!io_arm_poll_handler(req)) {
> + switch (io_arm_poll_handler(req)) {
> + case IO_ARM_POLL_READY:
> + goto issue_sqe;
Checked assembly, the fast path looks ok (i.e. not affected).
Also, a note, linked_timeout is handled correctly.
> + case IO_ARM_POLL_ERR:
> /*
> * Queued up for async execution, worker will release
> * submit reference when the iocb is actually submitted.
> */
> io_queue_async_work(req);
> + break;
> }
> } else {
> io_req_complete_failed(req, ret);
>
--
Pavel Begunkov
