On Fri, 1 Oct 2021 11:35:01 +0300 Tudor Cornea <tudor.cor...@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.cor...@gmail.com> Acked-by: Stephen Hemminger <step...@networkplumber.org>
