From: "Roger B. Melton" <rmelton@cisco.com>
To: Ferruh Yigit <ferruh.yigit@intel.com>,
Bruce Richardson <bruce.richardson@intel.com>
Cc: wenzhuo.lu@intel.com, dev@dpdk.org, "Ananyev,
Konstantin" <konstantin.ananyev@intel.com>
Subject: Re: [dpdk-dev] [PATCH v2] net/e1000: correct VLAN tag byte order for i35x LB packets
Date: Wed, 25 Oct 2017 16:45:13 -0400 [thread overview]
Message-ID: <6256a52f-43f1-3e3f-61af-932b4bd26955@cisco.com> (raw)
In-Reply-To: <cb73501f-ac53-308d-64f5-13dd6cbcd8a5@intel.com>
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@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?
I can tell you that from the perspective of my application the
performance impact for 1G is not a concern.
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.
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
>>
> .
>
next prev parent reply other threads:[~2017-10-25 20:45 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-12 17:24 Roger B Melton
2017-10-16 0:43 ` Lu, Wenzhuo
2017-10-25 21:37 ` Ferruh Yigit
2017-10-20 19:04 ` Ferruh Yigit
2017-10-23 17:42 ` Roger B. Melton
2017-10-25 18:11 ` Ferruh Yigit
2017-10-25 20:16 ` Bruce Richardson
2017-10-25 20:22 ` Ferruh Yigit
2017-10-25 20:45 ` Roger B. Melton [this message]
2017-10-25 20:48 ` Richardson, Bruce
2017-10-25 21:11 ` Ferruh Yigit
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