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

[Ferruh Yigit]

On 10/25/2017 1:48 PM, Richardson, Bruce wrote:
> 
> 
>> -----Original Message-----
>> From: Roger B. Melton [mailto:rmelton at cisco.com]
>> Sent: Wednesday, October 25, 2017 9:45 PM
>> To: Yigit, Ferruh <ferruh.yigit at intel.com>; Richardson, Bruce
>> <bruce.richardson at intel.com>
>> Cc: Lu, Wenzhuo <wenzhuo.lu at intel.com>; dev at dpdk.org; Ananyev, Konstantin
>> <konstantin.ananyev at intel.com>
>> Subject: Re: [dpdk-dev] [PATCH v2] net/e1000: correct VLAN tag byte order
>> for i35x LB packets
>>
>> On 10/25/17 4:22 PM, Ferruh Yigit wrote:
>>> On 10/25/2017 1:16 PM, Bruce Richardson wrote:
>>>> On Wed, Oct 25, 2017 at 11:11:08AM -0700, Ferruh Yigit wrote:
>>>>> 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?
>>>>>
>>>> For a 1G driver, is performance really that big an issue?
>>> I don't know. So is this an Ack from you for the patch?
> 
> No, I don't know much about this driver to comment. But it's an indication that
> I don't have any objections to it either. :-)
> 
>>
>> I can tell you that from the perspective of my application the performance
>> impact for 1G is not a concern.
> 
> That's kinda what I would expect.
> 
>>
>> FWIW, I did go through a few iterations with Wenzhou to minimize the
>> performance impact before we settled on this implementation, and Wenzhou
>> did Ack it btw.

Taking into account that Wenzhuo acked and there is no outstanding objection, I
will get this.

But I believe it would be good to run some regression tests on PMD after rc2.

>>
>> I'm hoping we can get this into 17.11.
>>
>> Thanks,
>> -Roger
>>
>>>
>>>> Unless you
>>>> have a *lot* of 1G ports, I would expect most platforms not to notice
>>>> an extra couple of cycles when dealing with 1G line rates.
>>>>
>>>> /Bruce
>>>>
>>> .
>>>
>