On Mon, Oct 28, 2024 at 03:17:07PM +0100, Martin Weiser wrote:
>
> The issue only appeared with hardware-timestamping enabled
> (RTE_ETH_RX_OFFLOAD_TIMESTAMP).
>
> The length of the prepended hardware timestamp was not subtracted from
> the data length so that received packets were 16 bytes longer than
> expected.
>
> In scatter-gather mode only the first mbuf has a timestamp but the
> data offset of the follow-up mbufs was not adjusted accordingly.
> This caused 16 bytes of packet data to be missing between
> the segments.
>
> Signed-off-by: Martin Weiser <martin.wei...@allegro-packets.com>
> ---
Hi,
thanks for the patch. Some comments inline below.
/Bruce
> drivers/net/igc/igc_txrx.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/net/igc/igc_txrx.c b/drivers/net/igc/igc_txrx.c
> index d0cee1b016..2fafa91bd5 100644
> --- a/drivers/net/igc/igc_txrx.c
> +++ b/drivers/net/igc/igc_txrx.c
> @@ -347,6 +347,8 @@ igc_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
> uint16_t nb_pkts)
>
> rxm->data_off = RTE_PKTMBUF_HEADROOM;
> data_len = rte_le_to_cpu_16(rxd.wb.upper.length) - rxq->crc_len;
> + if (rxq->offloads & RTE_ETH_RX_OFFLOAD_TIMESTAMP)
> + data_len -= IGC_TS_HDR_LEN;
> rxm->data_len = data_len;
> rxm->pkt_len = data_len;
> rxm->nb_segs = 1;
> @@ -509,6 +511,12 @@ igc_recv_scattered_pkts(void *rx_queue, struct rte_mbuf
> **rx_pkts,
> */
> rxm->data_off = RTE_PKTMBUF_HEADROOM;
> data_len = rte_le_to_cpu_16(rxd.wb.upper.length);
> + if (rxq->offloads & RTE_ETH_RX_OFFLOAD_TIMESTAMP) {
> + if (first_seg == NULL)
> + data_len -= IGC_TS_HDR_LEN;
> + else
> + rxm->data_off -= IGC_TS_HDR_LEN;
This initially confused me, because I was assuming that data_off was a typo
for data_len. However, then I realised on closer examination that, when
timestamp offload is enabled, the actual buffer addresses sent down to the
hardware are offset by IGC_TS_HDR_LEN (meaning the first buffer of a pkt
has the start of data at "normal" data_offset in mbuf, but subsequent
buffers need adjustment). Is my understanding of the issue correct?
In either case, I have two small bits of feedback on this:
* Firstly, I think this needs a comment explaining the logic here, to avoid
others being confused as I was.
* Secondly, a very minor point, but is the code clearer or shorter, if you
merge this extra code down into the next block which is already checking
for the first_segment of a packet or not?
> + }
> rxm->data_len = data_len;
>
> /*
> @@ -557,6 +565,7 @@ igc_recv_scattered_pkts(void *rx_queue, struct rte_mbuf
> **rx_pkts,
> last_seg->data_len = last_seg->data_len -
> (RTE_ETHER_CRC_LEN - data_len);
> last_seg->next = NULL;
> + rxm = last_seg;
> } else {
> rxm->data_len = (uint16_t)
> (data_len - RTE_ETHER_CRC_LEN);
> --
> 2.47.0
