Re: HW RX timestamp with LRO enabled on ConnectX-7 (DPDK 20.11)

[Yoon Junghan <cerotyki@gmail.com>]

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Thank you for your quick response!

FYI, I've already tried retrieving RX hardware timestamp without LRO, and confirmed it works well. Inter arrival time of packets was about 10ns~50ns in average.

I'll quickly check the references you attached.

Sincerely,
Junghan Yoon
On Jul 22, 2025, 5:31 PM +0900, Ivan Malov <ivan.malov@arknetworks.am>, wrote:
> Hello,
>
> On Tue, 22 Jul 2025, Yoon Junghan wrote:
>
> > Hello,
> >
> > I'm currently using DPDK 20.11 with a ConnectX-7 NIC, and I'm trying to retrieve RX hardware timestamps using `rte_mbuf_dyn_rx_timestamp_register()`.
>
> Does the application invoke 'rte_mbuf_dyn_rx_timestamp_register' on its own? If
> yes, consider to replace this with invocations of APIs [1] (with field name [2])
> and [3] (with flag name [4]). For an example, please refer to [5] and [6].
>
> This is because, as per [7], the driver in question might 'register' the field
> and the flag on its own, in response to 'DEV_RX_OFFLOAD_TIMESTAMP' request, so,
> the user application should look up the field/flag, not 'register' it afresh.
>
> If this does not help, then consider to clarify whether the timestamps are
> accurate (and whether the flag is seen in the mbufs) when LRO is not enabled.
>
> [1] https://doc.dpdk.org/api-20.11/rte__mbuf__dyn_8h.html#a6adf9b352a83e7d521fd6aa04e305b1c
> [2] https://doc.dpdk.org/api-20.11/rte__mbuf__dyn_8h.html#a5159b2d34fa801d171ed0ccce451121b
> [3] https://doc.dpdk.org/api-20.11/rte__mbuf__dyn_8h.html#a89d835027034f76a27eb2afe7987ae35
> [4] https://doc.dpdk.org/api-20.11/rte__mbuf__dyn_8h.html#a831d7066c7193788351797a65186848a
> [5] https://github.com/DPDK/dpdk/blob/d69724b1dcc69784bcef00b96597469b7f6e6207/app/test-pmd/util.c#L44
> [6] https://github.com/DPDK/dpdk/blob/d69724b1dcc69784bcef00b96597469b7f6e6207/app/test-pmd/util.c#L60
> [7] https://github.com/DPDK/dpdk/blob/d69724b1dcc69784bcef00b96597469b7f6e6207/drivers/net/mlx5/mlx5_rxq.c#L1743
>
> Thank you.
>
> >
> > When LRO is enabled, I notice that LROed mbufs seem to share identical timestamp values, and the timestamps are unexpectedly large or inconsistent. This raises the question of whether
> > LRO is interfering with the correctness of the RX HW timestamps.
> >
> > I’d appreciate any clarification on whether HW RX timestamping is reliable when LRO is enabled on this platform, or if LRO should be just disabled for accurate per-packet timestamping.
> >
> >
> > Sincerely,
> > Junghan Yoon
> >

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