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 <rmel...@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);
>> <...>
>> .
>>
>
>
