On 3/13/24 2:26 PM, Pavel Begunkov wrote:
> On 3/13/24 20:25, Jens Axboe wrote:
>> On 3/12/24 3:44 PM, David Wei wrote:
>>> Add an io_uring opcode OP_RECV_ZC for doing ZC reads from a socket that
>>> is set up for ZC Rx. The request reads skbs from a socket. Completions
>>> are posted into the main CQ for each page frag read.
>>>
>>> Big CQEs (CQE32) is required as the OP_RECV_ZC specific metadata (ZC
>>> region, offset, len) are stored in the extended 16 bytes as a
>>> struct io_uring_rbuf_cqe.
>>>
>>> For now there is no limit as to how much work each OP_RECV_ZC request
>>> does. It will attempt to drain a socket of all available data.
>>>
>>> Multishot requests are also supported. The first time an io_recvzc
>>> request completes, EAGAIN is returned which arms an async poll. Then, in
>>> subsequent runs in task work, IOU_ISSUE_SKIP_COMPLETE is returned to
>>> continue async polling.
>>
>> I'd probably drop that last paragraph, this is how all multishot
>> requests work and is implementation detail that need not go in the
>> commit message. Probably suffices just to say it supports multishot.
>>
>>> @@ -695,7 +701,7 @@ static inline bool io_recv_finish(struct io_kiocb *req, int *ret,
>>> unsigned int cflags;
>>> cflags = io_put_kbuf(req, issue_flags);
>>> - if (msg->msg_inq && msg->msg_inq != -1)
>>> + if (msg && msg->msg_inq && msg->msg_inq != -1)
>>> cflags |= IORING_CQE_F_SOCK_NONEMPTY;
>>> if (!(req->flags & REQ_F_APOLL_MULTISHOT)) {
>>> @@ -723,7 +729,7 @@ static inline bool io_recv_finish(struct io_kiocb *req, int *ret,
>>> goto enobufs;
>>> /* Known not-empty or unknown state, retry */
>>> - if (cflags & IORING_CQE_F_SOCK_NONEMPTY || msg->msg_inq == -1) {
>>> + if (cflags & IORING_CQE_F_SOCK_NONEMPTY || (msg && msg->msg_inq == -1)) {
>>> if (sr->nr_multishot_loops++ < MULTISHOT_MAX_RETRY)
>>> return false;
>>> /* mshot retries exceeded, force a requeue */
>>
>> Maybe refactor this a bit so that you don't need to add these NULL
>> checks? That seems pretty fragile, hard to read, and should be doable
>> without extra checks.
>
> That chunk can be completely thrown away, we're not using
> io_recv_finish() here anymore
>
>
>>> @@ -1053,6 +1058,85 @@ struct io_zc_rx_ifq *io_zc_verify_sock(struct io_kiocb *req,
>>> return ifq;
>>> }
>>> +int io_recvzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>>> +{
>>> + struct io_recvzc *zc = io_kiocb_to_cmd(req, struct io_recvzc);
>>> +
>>> + /* non-iopoll defer_taskrun only */
>>> + if (!req->ctx->task_complete)
>>> + return -EINVAL;
>>
>> What's the reasoning behind this?
>
> CQ locking, see the comment a couple lines below
>
>
>>> + struct io_recvzc *zc = io_kiocb_to_cmd(req, struct io_recvzc);
>>> + struct io_zc_rx_ifq *ifq;
>>> + struct socket *sock;
>>> + int ret;
>>> +
>>> + /*
>>> + * We're posting CQEs deeper in the stack, and to avoid taking CQ locks
>>> + * we serialise by having only the master thread modifying the CQ with
>>> + * DEFER_TASkRUN checked earlier and forbidding executing it from io-wq.
>>> + * That's similar to io_check_multishot() for multishot CQEs.
>>> + */
>
> This one ^^, though it doesn't read well, I should reword it for
> next time.
>
>>> + if (issue_flags & IO_URING_F_IOWQ)
>>> + return -EAGAIN;
>>> + if (WARN_ON_ONCE(!(issue_flags & IO_URING_F_NONBLOCK)))
>>> + return -EAGAIN;
>>
>> If rebased on the current tree, does this go away?
>
> It's just a little behind not to have that change
>
--
Jens Axboe
