Re: [dpdk-dev] [PATCH v2] net/e1000: correct VLAN tag byte order for i35x LB packets

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/12/2017 10:24 AM, Roger B Melton wrote:
> When copying VLAN tags from the RX descriptor to the vlan_tci field
> in the mbuf header,  igb_rxtx.c:eth_igb_recv_pkts() and
> eth_igb_recv_scattered_pkts() both assume that the VLAN tag is always
> little endian.  While i350, i354 and /i350vf VLAN non-loopback
> packets are stored little endian, VLAN tags in loopback packets for
> those devices are big endian.
> 
> For i350, i354 and i350vf VLAN loopback packets, swap the tag when
> copying from the RX descriptor to the mbuf header.  This will ensure
> that the mbuf vlan_tci is always little endian.
> 
> Signed-off-by: Roger B Melton <rmelton@cisco.com>

<...>

> @@ -946,9 +954,16 @@ eth_igb_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>  
>  		rxm->hash.rss = rxd.wb.lower.hi_dword.rss;
>  		hlen_type_rss = rte_le_to_cpu_32(rxd.wb.lower.lo_dword.data);
> -		/* Only valid if PKT_RX_VLAN_PKT set in pkt_flags */
> -		rxm->vlan_tci = rte_le_to_cpu_16(rxd.wb.upper.vlan);
> -
> +		/*
> +		 * The vlan_tci field is only valid when PKT_RX_VLAN_PKT is
> +		 * set in the pkt_flags field and must be in CPU byte order.
> +		 */
> +		if ((staterr & rte_cpu_to_le_32(E1000_RXDEXT_STATERR_LB)) &&
> +			(rxq->flags & IGB_RXQ_FLAG_LB_BSWAP_VLAN)) {

This is adding more condition checks into Rx path.
What is the performance cost of this addition?

> +			rxm->vlan_tci = rte_be_to_cpu_16(rxd.wb.upper.vlan);
> +		} else {
> +			rxm->vlan_tci = rte_le_to_cpu_16(rxd.wb.upper.vlan);
> +		}
>  		pkt_flags = rx_desc_hlen_type_rss_to_pkt_flags(rxq, hlen_type_rss);
>  		pkt_flags = pkt_flags | rx_desc_status_to_pkt_flags(staterr);
>  		pkt_flags = pkt_flags | rx_desc_error_to_pkt_flags(staterr);
<...>