Re: [dpdk-stable] [dpdk-dev] [PATCH v1 1/3] net/i40e: relax barrier in the Tx fastpath of vPMD

[Jerin Jacob <jerinjacobk@gmail.com>]

On Fri, Mar 6, 2020 at 10:35 AM Gavin Hu <gavin.hu@arm.com> wrote:
>
> To keep ordering of mixed accesses, rte_cio is sufficient.
> The rte_io barrier inside the I40E_PCI_REG_WRITE is overkill.[1]
>
> This patch fixes by replacing with just sufficient barriers in the
> normal PMD and vPMD.
>
> It showed 7% performance uplift on ThunderX2 and 4% on Arm N1SDP.
> The test case is the RFC2544 zero-loss test running testpmd.
>
> [1] http://inbox.dpdk.org/dev/CALBAE1M-ezVWCjqCZDBw+MMDEC4O9
> qf0Kpn89EMdGDajepKoZQ@mail.gmail.com
>
> Fixes: 4861cde46116 ("i40e: new poll mode driver")
> Cc: stable@dpdk.org
>
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>

Acked-by: Jerin Jacob <jerinj@marvell.com>



> ---
>  drivers/net/i40e/i40e_rxtx_vec_neon.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/i40e/i40e_rxtx_vec_neon.c b/drivers/net/i40e/i40e_rxtx_vec_neon.c
> index deb185fe2..4376d8911 100644
> --- a/drivers/net/i40e/i40e_rxtx_vec_neon.c
> +++ b/drivers/net/i40e/i40e_rxtx_vec_neon.c
> @@ -72,8 +72,9 @@ i40e_rxq_rearm(struct i40e_rx_queue *rxq)
>         rx_id = (uint16_t)((rxq->rxrearm_start == 0) ?
>                              (rxq->nb_rx_desc - 1) : (rxq->rxrearm_start - 1));
>
> +       rte_cio_wmb();
>         /* Update the tail pointer on the NIC */
> -       I40E_PCI_REG_WRITE(rxq->qrx_tail, rx_id);
> +       I40E_PCI_REG_WRITE_RELAXED(rxq->qrx_tail, rx_id);
>  }
>
>  static inline void
> @@ -564,7 +565,8 @@ i40e_xmit_fixed_burst_vec(void *tx_queue, struct rte_mbuf **tx_pkts,
>
>         txq->tx_tail = tx_id;
>
> -       I40E_PCI_REG_WRITE(txq->qtx_tail, txq->tx_tail);
> +       rte_cio_wmb();
> +       I40E_PCI_REG_WRITE_RELAXED(txq->qtx_tail, tx_id);
>
>         return nb_pkts;
>  }
> --
> 2.17.1
>