Hello, As advised, I tested hardware timestamps with LRO enabled on our ConnectX-7 NICs. However, the timestamps of LROed packets still show inconsistent and abnormally large gaps from normal packets. Interestingly, I found this issue does not appear on all CX-7 NICs. Even with identical DPDK code, firmware version (28.43.2566), and hardware models from the same manufacturer, only specific NICs exhibit this inconsistency. I have confirmed that: • All NICs use the same driver and firmware version. • All NICs are of the same model (MCX75310AAS-NEA_Ax). • The issue occurs only when LRO is enabled together with RX hardware timestamping. • Disabling LRO eliminates the issue. I would appreciate any insight into how this behavior can occur on only some ports despite same software and hardware setup. Below is my code snippet. ```c /*----------------------------------------------------------------------------*/ static inline int is_timestamp_enabled(struct rte_mbuf *mbuf) {    static uint64_t timestamp_rx_dynflag = 0;    int timestamp_rx_dynflag_offset;    if (!timestamp_rx_dynflag)    {        timestamp_rx_dynflag_offset =            rte_mbuf_dynflag_lookup(RTE_MBUF_DYNFLAG_RX_TIMESTAMP_NAME, NULL);        if (timestamp_rx_dynflag_offset < 0)        {            return 0;        }        timestamp_rx_dynflag = RTE_BIT64(timestamp_rx_dynflag_offset);    }    return mbuf->ol_flags & timestamp_rx_dynflag; } /*----------------------------------------------------------------------------*/ static inline rte_mbuf_timestamp_t * get_timestamp(struct rte_mbuf *mbuf) {    static int timestamp_dynfield_offset = -1;    if (timestamp_dynfield_offset < 0)    {        timestamp_dynfield_offset =            rte_mbuf_dynfield_lookup(RTE_MBUF_DYNFIELD_TIMESTAMP_NAME, NULL);        if (timestamp_dynfield_offset < 0)        {            return 0;        }    }    return RTE_MBUF_DYNFIELD(mbuf,                              timestamp_dynfield_offset,                              rte_mbuf_timestamp_t *); } /*----------------------------------------------------------------------------*/ static inline rte_mbuf_timestamp_t * get_rx_hw_timestamp(struct rte_mbuf *pkt) {    if (!is_timestamp_enabled(pkt))    {        printf("rx_hw_timestamp not enabled in mbuf!\n");        return NULL;    }    return get_timestamp(pkt); } ``` My DPDK application prints logs as below. ```c    /* parse HW timestamp */    rte_mbuf_timestamp_t *rx_timestamp = get_rx_hw_timestamp(pkt);    printf("[port %d] RX HW timestamp: %#016lx %s\n",           pctx->port_id,           *rx_timestamp,           pkt->ol_flags & PKT_RX_LRO ? "(LROed)" : "(not LROed)"); ``` Below are observations from two CX-7 ports under identical conditions. Normal NIC (port 0): [port 0] RX HW timestamp: 0x00007dcd2d185b (LROed) [port 0] RX HW timestamp: 0x00007dcd2d1911 (LROed) [port 0] RX HW timestamp: 0x00007dcd2d19c9 (LROed) [port 0] RX HW timestamp: 0x00007dcd2d37ca (LROed) [port 0] RX HW timestamp: 0x00007dcd2d4cb3 (not LROed) [port 0] RX HW timestamp: 0x00007dcd2d4cb3 (not LROed) [port 0] RX HW timestamp: 0x00007dcd30e019 (not LROed) [port 0] RX HW timestamp: 0x00007dcd3280bb (not LROed) Erroneous NIC (port 1): Below is erroneous NIC's timestamp. [port 1] RX HW timestamp: 0x3e6eef91bc19f0fd (LROed) [port 1] RX HW timestamp: 0x3e6eef91bc19f0fd (LROed) [port 1] RX HW timestamp: 0x3e6eef91bc19f0fd (LROed) [port 1] RX HW timestamp: 0x3e6eef91bc19f0fd (LROed) [port 1] RX HW timestamp: 0x000080691b7557 (not LROed) [port 1] RX HW timestamp: 0x000080691e2311 (not LROed) [port 1] RX HW timestamp: 0x00008069357553 (not LROed) [port 1] RX HW timestamp: 0x0000806936e8c1 (not LROed) As shown above, non-LRO packets consistently have normal hardware timestamps on both NICs. However, on port 1, all LROed packets return a fixed, invalid timestamp (0x3e6eef91bc19f0fd), which is clearly inconsistent. I have also confirmed that other dynfields (rather than dynfield[1] and dynfield[2]) are unused. Sincerely, Junghan Yoon On Jul 22, 2025, 5:31 PM +0900, Ivan Malov , 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 > >