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Message-ID: <6840ec0b351ee_1af4929492@willemb.c.googlers.com.notmuch>
Date: Wed, 04 Jun 2025 20:59:55 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Pavel Begunkov <asml.silence@...il.com>,
io-uring@...r.kernel.org,
Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: asml.silence@...il.com,
netdev@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>,
Kuniyuki Iwashima <kuniyu@...zon.com>,
Paolo Abeni <pabeni@...hat.com>,
Willem de Bruijn <willemb@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH v2 5/5] io_uring/netcmd: add tx timestamping cmd support
Pavel Begunkov wrote:
> Add a new socket command which returns tx time stamps to the user. It
> provide an alternative to the existing error queue recvmsg interface.
> The command works in a polled multishot mode, which means io_uring will
> poll the socket and keep posting timestamps until the request is
> cancelled or fails in any other way (e.g. with no space in the CQ). It
> reuses the net infra and grabs timestamps from the socket's error queue.
>
> The command requires IORING_SETUP_CQE32. All non-final CQEs (marked with
> IORING_CQE_F_MORE) have cqe->res set to the tskey, and the upper 16 bits
> of cqe->flags keep tstype (i.e. offset by IORING_CQE_BUFFER_SHIFT). The
> timevalue is store in the upper part of the extended CQE. The final
> completion won't have IORING_CQR_F_MORE and will have cqe->res storing
> 0/error.
>
> Suggested-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
> include/uapi/linux/io_uring.h | 6 +++
> io_uring/cmd_net.c | 77 +++++++++++++++++++++++++++++++++++
> 2 files changed, 83 insertions(+)
>
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index cfd17e382082..0bc156eb96d4 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -960,6 +960,11 @@ struct io_uring_recvmsg_out {
> __u32 flags;
> };
>
> +struct io_timespec {
> + __u64 tv_sec;
> + __u64 tv_nsec;
> +};
> +
> /*
> * Argument for IORING_OP_URING_CMD when file is a socket
> */
> @@ -968,6 +973,7 @@ enum io_uring_socket_op {
> SOCKET_URING_OP_SIOCOUTQ,
> SOCKET_URING_OP_GETSOCKOPT,
> SOCKET_URING_OP_SETSOCKOPT,
> + SOCKET_URING_OP_TX_TIMESTAMP,
> };
>
> /* Zero copy receive refill queue entry */
> diff --git a/io_uring/cmd_net.c b/io_uring/cmd_net.c
> index e99170c7d41a..dae59aea5847 100644
> --- a/io_uring/cmd_net.c
> +++ b/io_uring/cmd_net.c
> @@ -1,5 +1,6 @@
> #include <asm/ioctls.h>
> #include <linux/io_uring/net.h>
> +#include <linux/errqueue.h>
> #include <net/sock.h>
>
> #include "uring_cmd.h"
> @@ -51,6 +52,80 @@ static inline int io_uring_cmd_setsockopt(struct socket *sock,
> optlen);
> }
>
> +static bool io_process_timestamp_skb(struct io_uring_cmd *cmd, struct sock *sk,
> + struct sk_buff *skb, unsigned issue_flags)
> +{
> + struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
> + struct io_uring_cqe cqe[2];
> + struct io_timespec *iots;
> + struct timespec64 ts;
> + u32 tskey;
> +
> + BUILD_BUG_ON(sizeof(struct io_uring_cqe) != sizeof(struct io_timespec));
> +
> + if (!skb_get_tx_timestamp(skb, sk, &ts))
> + return false;
> +
> + tskey = serr->ee.ee_data;
> +
> + cqe->user_data = 0;
> + cqe->res = tskey;
> + cqe->flags = IORING_CQE_F_MORE;
> + cqe->flags |= (u32)serr->ee.ee_info << IORING_CQE_BUFFER_SHIFT;
> +
> + iots = (struct io_timespec *)&cqe[1];
> + iots->tv_sec = ts.tv_sec;
> + iots->tv_nsec = ts.tv_nsec;
skb_get_tx_timestamp loses the information whether this is a
software or a hardware timestamp. Is that loss problematic?
If a process only requests one type of timestamp, it will not be.
But when requesting both (SOF_TIMESTAMPING_OPT_TX_SWHW) this per cqe
annotation may be necessary.
> + return io_uring_cmd_post_mshot_cqe32(cmd, issue_flags, cqe);
> +}
> +
> +static int io_uring_cmd_timestamp(struct socket *sock,
> + struct io_uring_cmd *cmd,
> + unsigned int issue_flags)
> +{
> + struct sock *sk = sock->sk;
> + struct sk_buff_head *q = &sk->sk_error_queue;
> + struct sk_buff *skb, *tmp;
> + struct sk_buff_head list;
> + int ret;
> +
> + if (!(issue_flags & IO_URING_F_CQE32))
> + return -EINVAL;
> + ret = io_cmd_poll_multishot(cmd, issue_flags, EPOLLERR);
> + if (unlikely(ret))
> + return ret;
> +
> + if (skb_queue_empty_lockless(q))
> + return -EAGAIN;
> + __skb_queue_head_init(&list);
> +
> + scoped_guard(spinlock_irq, &q->lock) {
> + skb_queue_walk_safe(q, skb, tmp) {
> + /* don't support skbs with payload */
> + if (!skb_has_tx_timestamp(skb, sk) || skb->len)
> + continue;
> + __skb_unlink(skb, q);
> + __skb_queue_tail(&list, skb);
> + }
> + }
> +
> + while (1) {
> + skb = skb_peek(&list);
> + if (!skb)
> + break;
> + if (!io_process_timestamp_skb(cmd, sk, skb, issue_flags))
> + break;
> + __skb_dequeue(&list);
> + consume_skb(skb);
> + }
> +
> + if (!unlikely(skb_queue_empty(&list))) {
> + scoped_guard(spinlock_irqsave, &q->lock)
> + skb_queue_splice(q, &list);
> + }
> + return -EAGAIN;
> +}
> +
> int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
> {
> struct socket *sock = cmd->file->private_data;
> @@ -76,6 +151,8 @@ int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
> return io_uring_cmd_getsockopt(sock, cmd, issue_flags);
> case SOCKET_URING_OP_SETSOCKOPT:
> return io_uring_cmd_setsockopt(sock, cmd, issue_flags);
> + case SOCKET_URING_OP_TX_TIMESTAMP:
> + return io_uring_cmd_timestamp(sock, cmd, issue_flags);
> default:
> return -EOPNOTSUPP;
> }
> --
> 2.49.0
>
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