Re: [dpdk-dev] [PATCH v2] net/i40e: add logic of processing continuous DD bits for Arm

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>
> 
> For Arm platforms, reading descs can get re-ordered, then the status of DD
> bits will be discontinuous, so add the logic to only process continuous descs
> by checking DD bits.
> 
> Fixes: 4861cde46116 ("i40e: new poll mode driver")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> ---
>  drivers/net/i40e/i40e_rxtx.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c index
> 6c58decec..86e2f083e 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
> +482,22 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue *rxq)
>  					I40E_RXD_QW1_STATUS_SHIFT;
>  		}
> 
> -		rte_smp_rmb();
> +		/* This barrier is to order loads of different words in the
> descriptor */
> +		rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
I think this should go into a separate commit as the following change is unrelated.

> 
>  		/* 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);
> #ifdef
> +RTE_ARCH_ARM
> +			/* For Arm platforms, only compute continuous
> status bits */
> +			if (var)
> +				nb_dd += 1;
> +			else
> +				break;
> +#else
> +			nb_dd += var;
> +#endif
> +		}
> 
>  		nb_rx += nb_dd;
> 
> --
> 2.17.1