3. Flow Bifurcation How-to Guide

Flow Bifurcation is a mechanism which uses hardware capable Ethernet devices to split traffic between Linux user space and kernel space. Since it is a hardware assisted feature this approach can provide line rate processing capability. Other than KNI, the software is just required to enable device configuration, there is no need to take care of the packet movement during the traffic split. This can yield better performance with less CPU overhead.

The Flow Bifurcation splits the incoming data traffic to user space applications (such as DPDK applications) and/or kernel space programs (such as the Linux kernel stack). It can direct some traffic, for example data plane traffic, to DPDK, while directing some other traffic, for example control plane traffic, to the traditional Linux networking stack.

There are a number of technical options to achieve this. A typical example is to combine the technology of SR-IOV and packet classification filtering.

SR-IOV is a PCI standard that allows the same physical adapter to be split as multiple virtual functions. Each virtual function (VF) has separated queues with physical functions (PF). The network adapter will direct traffic to a virtual function with a matching destination MAC address. In a sense, SR-IOV has the capability for queue division.

Packet classification filtering is a hardware capability available on most network adapters. Filters can be configured to direct specific flows to a given receive queue by hardware. Different NICs may have different filter types to direct flows to a Virtual Function or a queue that belong to it.

In this way the Linux networking stack can receive specific traffic through the kernel driver while a DPDK application can receive specific traffic bypassing the Linux kernel by using drivers like VFIO or the DPDK igb_uio module.

Fig. 3.3 Flow Bifurcation Overview

3.1. Using Flow Bifurcation on Mellanox ConnectX

The Mellanox devices are natively bifurcated, so there is no need to split into SR-IOV PF/VF in order to get the flow bifurcation mechanism. The full device is already shared with the kernel driver.

The DPDK application can setup some flow steering rules, and let the rest go to the kernel stack. In order to define the filters strictly with flow rules, the Flow isolated mode can be configured.

There is no specific instructions to follow. The recommended reading is the Generic flow API (rte_flow) guide. Below is an example of testpmd commands for receiving VXLAN 42 in 4 queues of the DPDK port 0, while all other packets go to the kernel:

testpmd> flow isolate 0 true
testpmd> flow create 0 ingress pattern eth / ipv4 / udp / vxlan vni is 42 / end \
         actions rss queues 0 1 2 3 end / end

3.2. Using Flow Bifurcation on IXGBE in Linux

On Intel 82599 10 Gigabit Ethernet Controller series NICs Flow Bifurcation can be achieved by SR-IOV and Intel Flow Director technologies. Traffic can be directed to queues by the Flow Director capability, typically by matching 5-tuple of UDP/TCP packets.

The typical procedure to achieve this is as follows:

  1. Boot the system without iommu, or with iommu=pt.

  2. Create Virtual Functions:

    echo 2 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs
    
  3. Enable and set flow filters:

    ethtool -K eth1 ntuple on
    ethtool -N eth1 flow-type udp4 src-ip 192.0.2.2 dst-ip 198.51.100.2 \
            action $queue_index_in_VF0
    ethtool -N eth1 flow-type udp4 src-ip 198.51.100.2 dst-ip 192.0.2.2 \
            action $queue_index_in_VF1
    

    Where:

    • $queue_index_in_VFn: Bits 39:32 of the variable defines VF id + 1; the lower 32 bits indicates the queue index of the VF. Thus:
      • $queue_index_in_VF0 = (0x1 & 0xFF) << 32 + [queue index].
      • $queue_index_in_VF1 = (0x2 & 0xFF) << 32 + [queue index].
  4. Compile the DPDK application and insert igb_uio or probe the vfio-pci kernel modules as normal.

  5. Bind the virtual functions:

    modprobe vfio-pci
    dpdk-devbind.py -b vfio-pci 01:10.0
    dpdk-devbind.py -b vfio-pci 01:10.1
    
  6. Run a DPDK application on the VFs:

    testpmd -l 0-7 -n 4 -- -i -w 01:10.0 -w 01:10.1 --forward-mode=mac
    

In this example, traffic matching the rules will go through the VF by matching the filter rule. All other traffic, not matching the rules, will go through the default queue or scaling on queues in the PF. That is to say UDP packets with the specified IP source and destination addresses will go through the DPDK application. All other traffic, with different hosts or different protocols, will go through the Linux networking stack.

Note

3.3. Using Flow Bifurcation on I40E in Linux

On Intel X710/XL710 series Ethernet Controllers Flow Bifurcation can be achieved by SR-IOV, Cloud Filter and L3 VEB switch. The traffic can be directed to queues by the Cloud Filter and L3 VEB switch’s matching rule.

  • L3 VEB filters work for non-tunneled packets. It can direct a packet just by the Destination IP address to a queue in a VF.

  • Cloud filters work for the following types of tunneled packets.

    • Inner mac.
    • Inner mac + VNI.
    • Outer mac + Inner mac + VNI.
    • Inner mac + Inner vlan + VNI.
    • Inner mac + Inner vlan.

The typical procedure to achieve this is as follows:

  1. Boot the system without iommu, or with iommu=pt.

  2. Build and insert the i40e.ko module.

  3. Create Virtual Functions:

    echo 2 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs
    
  4. Add udp port offload to the NIC if using cloud filter:

    ip li add vxlan0 type vxlan id 42 group 239.1.1.1 local 10.16.43.214 dev <name>
    ifconfig vxlan0 up
    ip -d li show vxlan0
    

    Note

    Output such as add vxlan port 8472, index 0 success should be found in the system log.

  5. Examples of enabling and setting flow filters:

    • L3 VEB filter, for a route whose destination IP is 192.168.50.108 to VF 0’s queue 2.

      ethtool -N <dev_name> flow-type ip4 dst-ip 192.168.50.108 \
              user-def 0xffffffff00000000 action 2 loc 8
      
    • Inner mac, for a route whose inner destination mac is 0:0:0:0:9:0 to PF’s queue 6.

      ethtool -N <dev_name> flow-type ether dst 00:00:00:00:00:00 \
              m ff:ff:ff:ff:ff:ff src 00:00:00:00:09:00 m 00:00:00:00:00:00 \
              user-def 0xffffffff00000003 action 6 loc 1
      
    • Inner mac + VNI, for a route whose inner destination mac is 0:0:0:0:9:0 and VNI is 8 to PF’s queue 4.

      ethtool -N <dev_name> flow-type ether dst 00:00:00:00:00:00 \
              m ff:ff:ff:ff:ff:ff src 00:00:00:00:09:00 m 00:00:00:00:00:00 \
              user-def 0x800000003 action 4 loc 4
      
    • Outer mac + Inner mac + VNI, for a route whose outer mac is 68:05:ca:24:03:8b, inner destination mac is c2:1a:e1:53:bc:57, and VNI is 8 to PF’s queue 2.

      ethtool -N <dev_name> flow-type ether dst 68:05:ca:24:03:8b \
              m 00:00:00:00:00:00 src c2:1a:e1:53:bc:57 m 00:00:00:00:00:00 \
              user-def 0x800000003 action 2 loc 2
      
    • Inner mac + Inner vlan + VNI, for a route whose inner destination mac is 00:00:00:00:20:00, inner vlan is 10, and VNI is 8 to VF 0’s queue 1.

      ethtool -N <dev_name> flow-type ether dst 00:00:00:00:01:00 \
              m ff:ff:ff:ff:ff:ff src 00:00:00:00:20:00 m 00:00:00:00:00:00 \
              vlan 10 user-def 0x800000000 action 1 loc 5
      
    • Inner mac + Inner vlan, for a route whose inner destination mac is 00:00:00:00:20:00, and inner vlan is 10 to VF 0’s queue 1.

      ethtool -N <dev_name> flow-type ether dst 00:00:00:00:01:00 \
              m ff:ff:ff:ff:ff:ff src 00:00:00:00:20:00 m 00:00:00:00:00:00 \
              vlan 10 user-def 0xffffffff00000000 action 1 loc 5
      

    Note

    • If the upper 32 bits of ‘user-def’ are 0xffffffff, then the filter can be used for programming an L3 VEB filter, otherwise the upper 32 bits of ‘user-def’ can carry the tenant ID/VNI if specified/required.
    • Cloud filters can be defined with inner mac, outer mac, inner ip, inner vlan and VNI as part of the cloud tuple. It is always the destination (not source) mac/ip that these filters use. For all these examples dst and src mac address fields are overloaded dst == outer, src == inner.
    • The filter will direct a packet matching the rule to a vf id specified in the lower 32 bit of user-def to the queue specified by ‘action’.
    • If the vf id specified by the lower 32 bit of user-def is greater than or equal to max_vfs, then the filter is for the PF queues.
  6. Compile the DPDK application and insert igb_uio or probe the vfio-pci kernel modules as normal.

  7. Bind the virtual function:

    modprobe vfio-pci
    dpdk-devbind.py -b vfio-pci 01:10.0
    dpdk-devbind.py -b vfio-pci 01:10.1
    
  8. run DPDK application on VFs:

    testpmd -l 0-7 -n 4 -- -i -w 01:10.0 -w 01:10.1 --forward-mode=mac
    

Note

  • The above steps work on the i40e Linux kernel driver v1.5.16.
  • The Ethtool version used in this example is 3.18. The mask ff means ‘not involved’, while 00 or no mask means ‘involved’.
  • For more details of the configuration, refer to the cloud filter test plan