21. Link Bonding Poll Mode Driver Library

In addition to Poll Mode Drivers (PMDs) for physical and virtual hardware, DPDK also includes a pure-software library that allows physical PMDs to be bonded together to create a single logical PMD.

Fig. 21.1 Bonded PMDs

The Link Bonding PMD library(librte_pmd_bond) supports bonding of groups of rte_eth_dev ports of the same speed and duplex to provide similar capabilities to that found in Linux bonding driver to allow the aggregation of multiple (slave) NICs into a single logical interface between a server and a switch. The new bonded PMD will then process these interfaces based on the mode of operation specified to provide support for features such as redundant links, fault tolerance and/or load balancing.

The librte_pmd_bond library exports a C API which provides an API for the creation of bonded devices as well as the configuration and management of the bonded device and its slave devices.

Note

The Link Bonding PMD Library is enabled by default in the build configuration files, the library can be disabled by setting CONFIG_RTE_LIBRTE_PMD_BOND=n and recompiling the DPDK.

21.1. Link Bonding Modes Overview

Currently the Link Bonding PMD library supports following modes of operation:

Round-Robin (Mode 0):

Fig. 21.2 Round-Robin (Mode 0)

This mode provides load balancing and fault tolerance by transmission of packets in sequential order from the first available slave device through the last. Packets are bulk dequeued from devices then serviced in a round-robin manner. This mode does not guarantee in order reception of packets and down stream should be able to handle out of order packets.

Active Backup (Mode 1):

Fig. 21.3 Active Backup (Mode 1)

In this mode only one slave in the bond is active at any time, a different slave becomes active if, and only if, the primary active slave fails, thereby providing fault tolerance to slave failure. The single logical bonded interface’s MAC address is externally visible on only one NIC (port) to avoid confusing the network switch.

Balance XOR (Mode 2):

Fig. 21.4 Balance XOR (Mode 2)

This mode provides transmit load balancing (based on the selected transmission policy) and fault tolerance. The default policy (layer2) uses a simple calculation based on the packet flow source and destination MAC addresses as well as the number of active slaves available to the bonded device to classify the packet to a specific slave to transmit on. Alternate transmission policies supported are layer 2+3, this takes the IP source and destination addresses into the calculation of the transmit slave port and the final supported policy is layer 3+4, this uses IP source and destination addresses as well as the TCP/UDP source and destination port.

Note

The coloring differences of the packets are used to identify different flow classification calculated by the selected transmit policy

Broadcast (Mode 3):

Fig. 21.5 Broadcast (Mode 3)

This mode provides fault tolerance by transmission of packets on all slave ports.

Link Aggregation 802.3AD (Mode 4):

Fig. 21.6 Link Aggregation 802.3AD (Mode 4)

This mode provides dynamic link aggregation according to the 802.3ad specification. It negotiates and monitors aggregation groups that share the same speed and duplex settings using the selected balance transmit policy for balancing outgoing traffic.

DPDK implementation of this mode provide some additional requirements of the application.

It needs to call rte_eth_tx_burst and rte_eth_rx_burst with intervals period of less than 100ms.

Calls to rte_eth_tx_burst must have a buffer size of at least 2xN, where N is the number of slaves. This is a space required for LACP frames. Additionally LACP packets are included in the statistics, but they are not returned to the application.

Transmit Load Balancing (Mode 5):

Fig. 21.7 Transmit Load Balancing (Mode 5)

This mode provides an adaptive transmit load balancing. It dynamically changes the transmitting slave, according to the computed load. Statistics are collected in 100ms intervals and scheduled every 10ms.

21.2. Implementation Details

The librte_pmd_bond bonded device are compatible with the Ethernet device API exported by the Ethernet PMDs described in the DPDK API Reference.

The Link Bonding Library supports the creation of bonded devices at application startup time during EAL initialization using the --vdev option as well as programmatically via the C API rte_eth_bond_create function.

Bonded devices support the dynamical addition and removal of slave devices using the rte_eth_bond_slave_add / rte_eth_bond_slave_remove APIs.

After a slave device is added to a bonded device slave is stopped using rte_eth_dev_stop and then reconfigured using rte_eth_dev_configure the RX and TX queues are also reconfigured using rte_eth_tx_queue_setup / rte_eth_rx_queue_setup with the parameters use to configure the bonding device. If RSS is enabled for bonding device, this mode is also enabled on new slave and configured as well. Any flow which was configured to the bond device also is configured to the added slave.

Setting up multi-queue mode for bonding device to RSS, makes it fully RSS-capable, so all slaves are synchronized with its configuration. This mode is intended to provide RSS configuration on slaves transparent for client application implementation.

Bonding device stores its own version of RSS settings i.e. RETA, RSS hash function and RSS key, used to set up its slaves. That let to define the meaning of RSS configuration of bonding device as desired configuration of whole bonding (as one unit), without pointing any of slave inside. It is required to ensure consistency and made it more error-proof.

RSS hash function set for bonding device, is a maximal set of RSS hash functions supported by all bonded slaves. RETA size is a GCD of all its RETA’s sizes, so it can be easily used as a pattern providing expected behavior, even if slave RETAs’ sizes are different. If RSS Key is not set for bonded device, it’s not changed on the slaves and default key for device is used.

As RSS configurations, there is flow consistency in the bonded slaves for the next rte flow operations:

Validate:

Validate flow for each slave, failure at least for one slave causes to bond validation failure.

Create:

Create the flow in all slaves.
Save all the slaves created flows objects in bonding internal flow structure.
Failure in flow creation for existed slave rejects the flow.
Failure in flow creation for new slaves in slave adding time rejects the slave.

Destroy:

Destroy the flow in all slaves and release the bond internal flow memory.

Flush:

Destroy all the bonding PMD flows in all the slaves.

Note

Don’t call slaves flush directly, It destroys all the slave flows which may include external flows or the bond internal LACP flow.

Query:

Summarize flow counters from all the slaves, relevant only for RTE_FLOW_ACTION_TYPE_COUNT.

Isolate:

Call to flow isolate for all slaves.
Failure in flow isolation for existed slave rejects the isolate mode.
Failure in flow isolation for new slaves in slave adding time rejects the slave.

All settings are managed through the bonding port API and always are propagated in one direction (from bonding to slaves).

21.2.1. Link Status Change Interrupts / Polling

Link bonding devices support the registration of a link status change callback, using the rte_eth_dev_callback_register API, this will be called when the status of the bonding device changes. For example in the case of a bonding device which has 3 slaves, the link status will change to up when one slave becomes active or change to down when all slaves become inactive. There is no callback notification when a single slave changes state and the previous conditions are not met. If a user wishes to monitor individual slaves then they must register callbacks with that slave directly.

The link bonding library also supports devices which do not implement link status change interrupts, this is achieved by polling the devices link status at a defined period which is set using the rte_eth_bond_link_monitoring_set API, the default polling interval is 10ms. When a device is added as a slave to a bonding device it is determined using the RTE_PCI_DRV_INTR_LSC flag whether the device supports interrupts or whether the link status should be monitored by polling it.

21.2.2. Requirements / Limitations

The current implementation only supports devices that support the same speed and duplex to be added as a slaves to the same bonded device. The bonded device inherits these attributes from the first active slave added to the bonded device and then all further slaves added to the bonded device must support these parameters.

A bonding device must have a minimum of one slave before the bonding device itself can be started.

To use a bonding device dynamic RSS configuration feature effectively, it is also required, that all slaves should be RSS-capable and support, at least one common hash function available for each of them. Changing RSS key is only possible, when all slave devices support the same key size.

To prevent inconsistency on how slaves process packets, once a device is added to a bonding device, RSS and rte flow configurations should be managed through the bonding device API, and not directly on the slave.

Like all other PMD, all functions exported by a PMD are lock-free functions that are assumed not to be invoked in parallel on different logical cores to work on the same target object.

It should also be noted that the PMD receive function should not be invoked directly on a slave devices after they have been to a bonded device since packets read directly from the slave device will no longer be available to the bonded device to read.

21.2.3. Configuration

Link bonding devices are created using the rte_eth_bond_create API which requires a unique device name, the bonding mode, and the socket Id to allocate the bonding device’s resources on. The other configurable parameters for a bonded device are its slave devices, its primary slave, a user defined MAC address and transmission policy to use if the device is in balance XOR mode.

21.2.3.1. Slave Devices

Bonding devices support up to a maximum of RTE_MAX_ETHPORTS slave devices of the same speed and duplex. Ethernet devices can be added as a slave to a maximum of one bonded device. Slave devices are reconfigured with the configuration of the bonded device on being added to a bonded device.

The bonded also guarantees to return the MAC address of the slave device to its original value of removal of a slave from it.

21.2.3.2. Primary Slave

The primary slave is used to define the default port to use when a bonded device is in active backup mode. A different port will only be used if, and only if, the current primary port goes down. If the user does not specify a primary port it will default to being the first port added to the bonded device.

21.2.3.3. MAC Address

The bonded device can be configured with a user specified MAC address, this address will be inherited by the some/all slave devices depending on the operating mode. If the device is in active backup mode then only the primary device will have the user specified MAC, all other slaves will retain their original MAC address. In mode 0, 2, 3, 4 all slaves devices are configure with the bonded devices MAC address.

If a user defined MAC address is not defined then the bonded device will default to using the primary slaves MAC address.

21.2.3.4. Balance XOR Transmit Policies

There are 3 supported transmission policies for bonded device running in Balance XOR mode. Layer 2, Layer 2+3, Layer 3+4.

Layer 2: Ethernet MAC address based balancing is the default transmission policy for Balance XOR bonding mode. It uses a simple XOR calculation on the source MAC address and destination MAC address of the packet and then calculate the modulus of this value to calculate the slave device to transmit the packet on.
Layer 2 + 3: Ethernet MAC address & IP Address based balancing uses a combination of source/destination MAC addresses and the source/destination IP addresses of the data packet to decide which slave port the packet will be transmitted on.
Layer 3 + 4: IP Address & UDP Port based balancing uses a combination of source/destination IP Address and the source/destination UDP ports of the packet of the data packet to decide which slave port the packet will be transmitted on.

All these policies support 802.1Q VLAN Ethernet packets, as well as IPv4, IPv6 and UDP protocols for load balancing.

21.3. Using Link Bonding Devices

The librte_pmd_bond library supports two modes of device creation, the libraries export full C API or using the EAL command line to statically configure link bonding devices at application startup. Using the EAL option it is possible to use link bonding functionality transparently without specific knowledge of the libraries API, this can be used, for example, to add bonding functionality, such as active backup, to an existing application which has no knowledge of the link bonding C API.

21.3.1. Using the Poll Mode Driver from an Application

Using the librte_pmd_bond libraries API it is possible to dynamically create and manage link bonding device from within any application. Link bonding devices are created using the rte_eth_bond_create API which requires a unique device name, the link bonding mode to initial the device in and finally the socket Id which to allocate the devices resources onto. After successful creation of a bonding device it must be configured using the generic Ethernet device configure API rte_eth_dev_configure and then the RX and TX queues which will be used must be setup using rte_eth_tx_queue_setup / rte_eth_rx_queue_setup.

Slave devices can be dynamically added and removed from a link bonding device using the rte_eth_bond_slave_add / rte_eth_bond_slave_remove APIs but at least one slave device must be added to the link bonding device before it can be started using rte_eth_dev_start.

The link status of a bonded device is dictated by that of its slaves, if all slave device link status are down or if all slaves are removed from the link bonding device then the link status of the bonding device will go down.

It is also possible to configure / query the configuration of the control parameters of a bonded device using the provided APIs rte_eth_bond_mode_set/ get, rte_eth_bond_primary_set/get, rte_eth_bond_mac_set/reset and rte_eth_bond_xmit_policy_set/get.

21.3.2. Using Link Bonding Devices from the EAL Command Line

Link bonding devices can be created at application startup time using the --vdev EAL command line option. The device name must start with the net_bonding prefix followed by numbers or letters. The name must be unique for each device. Each device can have multiple options arranged in a comma separated list. Multiple devices definitions can be arranged by calling the --vdev option multiple times.

Device names and bonding options must be separated by commas as shown below:

$RTE_TARGET/app/testpmd -l 0-3 -n 4 --vdev 'net_bonding0,bond_opt0=..,bond opt1=..'--vdev 'net_bonding1,bond _opt0=..,bond_opt1=..'

21.3.2.1. Link Bonding EAL Options

There are multiple ways of definitions that can be assessed and combined as long as the following two rules are respected:

A unique device name, in the format of net_bondingX is provided, where X can be any combination of numbers and/or letters, and the name is no greater than 32 characters long.
A least one slave device is provided with for each bonded device definition.
The operation mode of the bonded device being created is provided.

The different options are:

mode: Integer value defining the bonding mode of the device. Currently supports modes 0,1,2,3,4,5 (round-robin, active backup, balance, broadcast, link aggregation, transmit load balancing).

mode=2

slave: Defines the PMD device which will be added as slave to the bonded device. This option can be selected multiple times, for each device to be added as a slave. Physical devices should be specified using their PCI address, in the format domain:bus:devid.function

slave=0000:0a:00.0,slave=0000:0a:00.1

primary: Optional parameter which defines the primary slave port, is used in active backup mode to select the primary slave for data TX/RX if it is available. The primary port also is used to select the MAC address to use when it is not defined by the user. This defaults to the first slave added to the device if it is specified. The primary device must be a slave of the bonded device.

primary=0000:0a:00.0

socket_id: Optional parameter used to select which socket on a NUMA device the bonded devices resources will be allocated on.

socket_id=0

mac: Optional parameter to select a MAC address for link bonding device, this overrides the value of the primary slave device.

mac=00:1e:67:1d:fd:1d

xmit_policy: Optional parameter which defines the transmission policy when the bonded device is in balance mode. If not user specified this defaults to l2 (layer 2) forwarding, the other transmission policies available are l23 (layer 2+3) and l34 (layer 3+4)

xmit_policy=l23

lsc_poll_period_ms: Optional parameter which defines the polling interval in milli-seconds at which devices which don’t support lsc interrupts are checked for a change in the devices link status

lsc_poll_period_ms=100

up_delay: Optional parameter which adds a delay in milli-seconds to the propagation of a devices link status changing to up, by default this parameter is zero.

up_delay=10

down_delay: Optional parameter which adds a delay in milli-seconds to the propagation of a devices link status changing to down, by default this parameter is zero.

down_delay=50

21.3.2.2. Examples of Usage

Create a bonded device in round robin mode with two slaves specified by their PCI address:

$RTE_TARGET/app/testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=0,slave=0000:0a:00.01,slave=0000:04:00.00' -- --port-topology=chained

Create a bonded device in round robin mode with two slaves specified by their PCI address and an overriding MAC address:

$RTE_TARGET/app/testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=0,slave=0000:0a:00.01,slave=0000:04:00.00,mac=00:1e:67:1d:fd:1d' -- --port-topology=chained

Create a bonded device in active backup mode with two slaves specified, and a primary slave specified by their PCI addresses:

$RTE_TARGET/app/testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=1,slave=0000:0a:00.01,slave=0000:04:00.00,primary=0000:0a:00.01' -- --port-topology=chained

Create a bonded device in balance mode with two slaves specified by their PCI addresses, and a transmission policy of layer 3 + 4 forwarding:

$RTE_TARGET/app/testpmd -l 0-3 -n 4 --vdev 'net_bonding0,mode=2,slave=0000:0a:00.01,slave=0000:04:00.00,xmit_policy=l34' -- --port-topology=chained