Re: [PATCH v2 5/5] io_uring/netcmd: add tx timestamping cmd support

[Jason Xing <kerneljasonxing@gmail.com>]

On Fri, Jun 6, 2025 at 4:11 PM Pavel Begunkov <asml.silence@gmail.com> wrote:
>
> On 6/6/25 01:02, Jason Xing wrote:
> ...>>>>                                 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.
> >>
> >> skb_has_tx_timestamp() helper has clear priority of software timestamp,
> >> if enabled for the socket. Looks like SOF_TIMESTAMPING_OPT_TX_SWHW case
> >> won't produce both timestamps with the current implementation. Am I
> >> missing something?
> >
> > Sorry that I don't know how iouring works at a high level, so my
> > question could be naive and unrelated to what Willem said.
> >
> > Is it possible that applications set various tx sw timestamp flags
> > (like SOF_TIMESTAMPING_TX_SCHED, SOF_TIMESTAMPING_TX_SOFTWARE)? If it
>
> io_uring takes timestamps from the error queue, just like the socket
> api does it. There should be different skbs in the queue for different
> SCM_TSTAMP_{SND,SCHED,ACK,*} timestamps, io_uring only passes the
> type it got in an skb's serr->ee.ee_info to user without changes.
> Hope it answers it

Sure, thanks, io_uring has no difference from other regular
applications in this case. Then the question that Willem proposed
remains because in other applications struct scm_timestamping_internal
can be used to distinguish sw and hw timestamps (please see
__sock_recv_timestamp() as an example).

Thanks,
Jason