> -----Original Message-----
> From: Joyce Kong <joyce.k...@arm.com>
> Sent: Friday, June 4, 2021 3:34 PM
> To: Xing, Beilei <beilei.x...@intel.com>; Zhang, Qi Z <qi.z.zh...@intel.com>;
> ruifeng.w...@arm.com; honnappa.nagaraha...@arm.com
> Cc: dev@dpdk.org; n...@arm.com
> Subject: [PATCH v1] net/i40e: remove the SMP barrier in HW scanning func
>
> Add the logic to determine how many DD bits have been set for contiguous
> packets, for removing the SMP barrier while reading descs.
I didn't understand this.
The current logic already guarantee the read out DD bits are from continue
packets, as it read Rx descriptor in a reversed order from the ring.
So I didn't see the a new logic be added, would you describe more clear about
the purpose of this patch?
>
> Signed-off-by: Joyce Kong <joyce.k...@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> ---
> drivers/net/i40e/i40e_rxtx.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c index
> 6c58decec..410a81f30 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -452,7 +452,7 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
> uint16_t pkt_len;
> uint64_t qword1;
> uint32_t rx_status;
> - int32_t s[I40E_LOOK_AHEAD], nb_dd;
> + int32_t s[I40E_LOOK_AHEAD], var, nb_dd;
> int32_t i, j, nb_rx = 0;
> uint64_t pkt_flags;
> uint32_t *ptype_tbl = rxq->vsi->adapter->ptype_tbl; @@ -482,11 +482,14
> @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
> I40E_RXD_QW1_STATUS_SHIFT;
> }
>
> - rte_smp_rmb();
Any performance gain by removing this? and it is not necessary to be combined
with below change, right?
> -
> /* Compute how many status bits were set */
> - for (j = 0, nb_dd = 0; j < I40E_LOOK_AHEAD; j++)
> - nb_dd += s[j] & (1 << I40E_RX_DESC_STATUS_DD_SHIFT);
> + for (j = 0, nb_dd = 0; j < I40E_LOOK_AHEAD; j++) {
> + var = s[j] & (1 << I40E_RX_DESC_STATUS_DD_SHIFT);
> + if (var)
> + nb_dd += 1;
> + else
> + break;
> + }
>
> nb_rx += nb_dd;
>
> --
> 2.17.1
