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

[Ferruh Yigit]

On 10/23/2017 10:42 AM, Roger B. Melton wrote:
> On 10/20/17 3:04 PM, Ferruh Yigit wrote:
>> 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 at 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?
> 
> I have not measured the performance cost, but I can collect data. What 
> specifically are you looking for?
> 
> To be clear the current implementation incorrect as it does not 
> normalize the vlan tag to CPU byte order before copying it into mbuf and 
> applications have no visibility to determine if the tag in the mbuf is 
> big or little endian.
> 
> Do you have any suggestions for an alternative approach to avoid rx 
> patch checks?

No suggestion indeed. And correctness matters.

But this add a cost and I wonder how much it is, based on that result it may be
possible to do more investigation for alternate solutions or trade-offs.

Konstantin, Bruce, Wenzhuo,

What do you think, do you have any comment?

Thanks,
ferruh

> 
> Thanks,
> Roger
> 
> 
>>
>>> +			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);
>> <...>
>> .
>>
> 
>