[dpdk-dev] [PATCH v5] net/af_packet: reinsert the stripped vlan tag

[Ferruh Yigit]

On 10/1/2021 4:02 PM, Stephen Hemminger wrote:
> On Fri,  1 Oct 2021 11:35:01 +0300
> Tudor Cornea <tudor.cornea at gmail.com> wrote:
> 
>> The af_packet pmd driver binds to a raw socket and allows
>> sending and receiving of packets through the kernel.
>>
>> Since commit [1], the kernel strips the vlan tags early in
>> __netif_receive_skb_core(), so we receive untagged packets while
>> running with the af_packet pmd.
>>
>> Luckily for us, the skb vlan-related fields are still populated from the
>> stripped vlan tags, so we end up having all the information
>> that we need in the mbuf.
>>
>> Having the pmd driver support DEV_RX_OFFLOAD_VLAN_STRIP allows the
>> application to control the desired vlan stripping behavior,
>> until we have a way to describe offloads that can't be disabled by
>> pmd drivers.
>>
>> This patch will cause a change in the default way that the af_packet
>> pmd treats received vlan-tagged frames. While previously, the
>> application was required to check the PKT_RX_VLAN_STRIPPED flag, after
>> this patch, the pmd will re-insert the vlan tag transparently to the
>> user, unless the DEV_RX_OFFLOAD_VLAN_STRIP is enabled in
>> rxmode.offloads.
>>
>> I've attempted a preliminary benchmark to understand if the change could
>> cause a sizable performance hit.
>>
>> Setup:
>> Two virtual machines running on top of an ESXi hypervisor
>>
>> Tx: DPDK app (running on top of vmxnet3 PMD)
>> Rx: af_packet (running on top of a kernel vmxnet3 interface)
>> Packet size :68 (packet contains a vlan tag)
>>
>> Rates:
>> Tx - 1.419 Mpps
>> Rx (without vlan insertion) - 1227636 pps
>> Rx (with vlan insertion)    - 1220081 pps
>>
>> At a first glance, we don't seem to have a large degradation in terms
>> of packet rate.
>>
>> [1] https://github.com/torvalds/linux/commit/bcc6d47903612c3861201cc3a866fb604f26b8b2
>>
>> Signed-off-by: Tudor Cornea <tudor.cornea at gmail.com>
> 
> 
> Acked-by: Stephen Hemminger <stephen at networkplumber.org>
> 

Acked-by: Ferruh Yigit <ferruh.yigit at intel.com>

Applied to dpdk-next-net/main, thanks.
Release notes slightly updated, to simplify the sentences, while merging.