13. MLX5 poll mode driver

The MLX5 poll mode driver library (librte_pmd_mlx5) provides support for Mellanox ConnectX-4, Mellanox ConnectX-4 Lx and Mellanox ConnectX-5 families of 10/25/40/50/100 Gb/s adapters as well as their virtual functions (VF) in SR-IOV context.

Information and documentation about these adapters can be found on the Mellanox website. Help is also provided by the Mellanox community.

There is also a section dedicated to this poll mode driver.


Due to external dependencies, this driver is disabled by default. It must be enabled manually by setting CONFIG_RTE_LIBRTE_MLX5_PMD=y and recompiling DPDK.

13.1. Implementation details

Besides its dependency on libibverbs (that implies libmlx5 and associated kernel support), librte_pmd_mlx5 relies heavily on system calls for control operations such as querying/updating the MTU and flow control parameters.

For security reasons and robustness, this driver only deals with virtual memory addresses. The way resources allocations are handled by the kernel combined with hardware specifications that allow it to handle virtual memory addresses directly ensure that DPDK applications cannot access random physical memory (or memory that does not belong to the current process).

This capability allows the PMD to coexist with kernel network interfaces which remain functional, although they stop receiving unicast packets as long as they share the same MAC address.

Enabling librte_pmd_mlx5 causes DPDK applications to be linked against libibverbs.

13.2. Features

  • Multiple TX and RX queues.
  • Support for scattered TX and RX frames.
  • IPv4, IPv6, TCPv4, TCPv6, UDPv4 and UDPv6 RSS on any number of queues.
  • Several RSS hash keys, one for each flow type.
  • Configurable RETA table.
  • Support for multiple MAC addresses.
  • VLAN filtering.
  • RX VLAN stripping.
  • TX VLAN insertion.
  • RX CRC stripping configuration.
  • Promiscuous mode.
  • Multicast promiscuous mode.
  • Hardware checksum offloads.
  • Flow API.
  • Secondary process TX is supported.
  • KVM and VMware ESX SR-IOV modes are supported.
  • RSS hash result is supported.

13.3. Limitations

  • Inner RSS for VXLAN frames is not supported yet.
  • Port statistics through software counters only.
  • Hardware checksum offloads for VXLAN inner header are not supported yet.
  • Secondary process RX is not supported.

13.4. Configuration

13.4.1. Compilation options

These options can be modified in the .config file.

  • CONFIG_RTE_LIBRTE_MLX5_PMD (default n)

    Toggle compilation of librte_pmd_mlx5 itself.


    Toggle debugging code and stricter compilation flags. Enabling this option adds additional run-time checks and debugging messages at the cost of lower performance.


    Maximum number of cached memory pools (MPs) per TX queue. Each MP from which buffers are to be transmitted must be associated to memory regions (MRs). This is a slow operation that must be cached.

    This value is always 1 for RX queues since they use a single MP.

13.4.2. Environment variables


    Enables HW packet padding in PCI bus transactions.

    When packet size is cache aligned and CRC stripping is enabled, 4 fewer bytes are written to the PCI bus. Enabling padding makes such packets aligned again.

    In cases where PCI bandwidth is the bottleneck, padding can improve performance by 10%.

    This is disabled by default since this can also decrease performance for unaligned packet sizes.

13.4.3. Run-time configuration

  • librte_pmd_mlx5 brings kernel network interfaces up during initialization because it is affected by their state. Forcing them down prevents packets reception.

  • ethtool operations on related kernel interfaces also affect the PMD.

  • rxq_cqe_comp_en parameter [int]

    A nonzero value enables the compression of CQE on RX side. This feature allows to save PCI bandwidth and improve performance at the cost of a slightly higher CPU usage. Enabled by default.

    Supported on:

    • x86_64 with ConnectX4 and ConnectX4 LX
    • Power8 with ConnectX4 LX
  • txq_inline parameter [int]

    Amount of data to be inlined during TX operations. Improves latency. Can improve PPS performance when PCI back pressure is detected and may be useful for scenarios involving heavy traffic on many queues.

    It is not enabled by default (set to 0) since the additional software logic necessary to handle this mode can lower performance when back pressure is not expected.

  • txqs_min_inline parameter [int]

    Enable inline send only when the number of TX queues is greater or equal to this value.

    This option should be used in combination with txq_inline above.

  • txq_mpw_en parameter [int]

    A nonzero value enables multi-packet send. This feature allows the TX burst function to pack up to five packets in two descriptors in order to save PCI bandwidth and improve performance at the cost of a slightly higher CPU usage.

    It is currently only supported on the ConnectX-4 Lx and ConnectX-5 families of adapters. Enabled by default.

13.5. Prerequisites

This driver relies on external libraries and kernel drivers for resources allocations and initialization. The following dependencies are not part of DPDK and must be installed separately:

  • libibverbs

    User space Verbs framework used by librte_pmd_mlx5. This library provides a generic interface between the kernel and low-level user space drivers such as libmlx5.

    It allows slow and privileged operations (context initialization, hardware resources allocations) to be managed by the kernel and fast operations to never leave user space.

  • libmlx5

    Low-level user space driver library for Mellanox ConnectX-4/ConnectX-5 devices, it is automatically loaded by libibverbs.

    This library basically implements send/receive calls to the hardware queues.

  • Kernel modules (mlnx-ofed-kernel)

    They provide the kernel-side Verbs API and low level device drivers that manage actual hardware initialization and resources sharing with user space processes.

    Unlike most other PMDs, these modules must remain loaded and bound to their devices:

    • mlx5_core: hardware driver managing Mellanox ConnectX-4/ConnectX-5 devices and related Ethernet kernel network devices.
    • mlx5_ib: InifiniBand device driver.
    • ib_uverbs: user space driver for Verbs (entry point for libibverbs).
  • Firmware update

    Mellanox OFED releases include firmware updates for ConnectX-4/ConnectX-5 adapters.

    Because each release provides new features, these updates must be applied to match the kernel modules and libraries they come with.


Both libraries are BSD and GPL licensed. Linux kernel modules are GPL licensed.

Currently supported by DPDK:

  • Mellanox OFED version: 4.0-
  • firmware version:
    • ConnectX-4: 12.18.1000
    • ConnectX-4 Lx: 14.18.1000
    • ConnectX-5: 16.18.1000
    • ConnectX-5 Ex: 16.18.1000

13.5.1. Getting Mellanox OFED

While these libraries and kernel modules are available on OpenFabrics Alliance’s website and provided by package managers on most distributions, this PMD requires Ethernet extensions that may not be supported at the moment (this is a work in progress).

Mellanox OFED includes the necessary support and should be used in the meantime. For DPDK, only libibverbs, libmlx5, mlnx-ofed-kernel packages and firmware updates are required from that distribution.


Several versions of Mellanox OFED are available. Installing the version this DPDK release was developed and tested against is strongly recommended. Please check the prerequisites.

13.6. Supported NICs

  • Mellanox(R) ConnectX(R)-4 10G MCX4111A-XCAT (1x10G)
  • Mellanox(R) ConnectX(R)-4 10G MCX4121A-XCAT (2x10G)
  • Mellanox(R) ConnectX(R)-4 25G MCX4111A-ACAT (1x25G)
  • Mellanox(R) ConnectX(R)-4 25G MCX4121A-ACAT (2x25G)
  • Mellanox(R) ConnectX(R)-4 40G MCX4131A-BCAT (1x40G)
  • Mellanox(R) ConnectX(R)-4 40G MCX413A-BCAT (1x40G)
  • Mellanox(R) ConnectX(R)-4 40G MCX415A-BCAT (1x40G)
  • Mellanox(R) ConnectX(R)-4 50G MCX4131A-GCAT (1x50G)
  • Mellanox(R) ConnectX(R)-4 50G MCX413A-GCAT (1x50G)
  • Mellanox(R) ConnectX(R)-4 50G MCX414A-BCAT (2x50G)
  • Mellanox(R) ConnectX(R)-4 50G MCX415A-GCAT (2x50G)
  • Mellanox(R) ConnectX(R)-4 50G MCX416A-BCAT (2x50G)
  • Mellanox(R) ConnectX(R)-4 50G MCX416A-GCAT (2x50G)
  • Mellanox(R) ConnectX(R)-4 50G MCX415A-CCAT (1x100G)
  • Mellanox(R) ConnectX(R)-4 100G MCX416A-CCAT (2x100G)
  • Mellanox(R) ConnectX(R)-4 Lx 10G MCX4121A-XCAT (2x10G)
  • Mellanox(R) ConnectX(R)-4 Lx 25G MCX4121A-ACAT (2x25G)
  • Mellanox(R) ConnectX(R)-5 100G MCX556A-ECAT (2x100G)
  • Mellanox(R) ConnectX(R)-5 Ex EN 100G MCX516A-CDAT (2x100G)

13.7. Notes for testpmd

Compared to librte_pmd_mlx4 that implements a single RSS configuration per port, librte_pmd_mlx5 supports per-protocol RSS configuration.

Since testpmd defaults to IP RSS mode and there is currently no command-line parameter to enable additional protocols (UDP and TCP as well as IP), the following commands must be entered from its CLI to get the same behavior as librte_pmd_mlx4:

> port stop all
> port config all rss all
> port start all

13.8. Usage example

This section demonstrates how to launch testpmd with Mellanox ConnectX-4/ConnectX-5 devices managed by librte_pmd_mlx5.

  1. Load the kernel modules:

    modprobe -a ib_uverbs mlx5_core mlx5_ib

    Alternatively if MLNX_OFED is fully installed, the following script can be run:

    /etc/init.d/openibd restart


    User space I/O kernel modules (uio and igb_uio) are not used and do not have to be loaded.

  2. Make sure Ethernet interfaces are in working order and linked to kernel verbs. Related sysfs entries should be present:

    ls -d /sys/class/net/*/device/infiniband_verbs/uverbs* | cut -d / -f 5

    Example output:

  3. Optionally, retrieve their PCI bus addresses for whitelisting:

        for intf in eth2 eth3 eth4 eth5;
            (cd "/sys/class/net/${intf}/device/" && pwd -P);
    } |
    sed -n 's,.*/\(.*\),-w \1,p'

    Example output:

    -w 0000:05:00.1
    -w 0000:06:00.0
    -w 0000:06:00.1
    -w 0000:05:00.0
  4. Request huge pages:

    echo 1024 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages/nr_hugepages
  5. Start testpmd with basic parameters:

    testpmd -c 0xff00 -n 4 -w 05:00.0 -w 05:00.1 -w 06:00.0 -w 06:00.1 -- --rxq=2 --txq=2 -i

    Example output:

    EAL: PCI device 0000:05:00.0 on NUMA socket 0
    EAL:   probe driver: 15b3:1013 librte_pmd_mlx5
    PMD: librte_pmd_mlx5: PCI information matches, using device "mlx5_0" (VF: false)
    PMD: librte_pmd_mlx5: 1 port(s) detected
    PMD: librte_pmd_mlx5: port 1 MAC address is e4:1d:2d:e7:0c:fe
    EAL: PCI device 0000:05:00.1 on NUMA socket 0
    EAL:   probe driver: 15b3:1013 librte_pmd_mlx5
    PMD: librte_pmd_mlx5: PCI information matches, using device "mlx5_1" (VF: false)
    PMD: librte_pmd_mlx5: 1 port(s) detected
    PMD: librte_pmd_mlx5: port 1 MAC address is e4:1d:2d:e7:0c:ff
    EAL: PCI device 0000:06:00.0 on NUMA socket 0
    EAL:   probe driver: 15b3:1013 librte_pmd_mlx5
    PMD: librte_pmd_mlx5: PCI information matches, using device "mlx5_2" (VF: false)
    PMD: librte_pmd_mlx5: 1 port(s) detected
    PMD: librte_pmd_mlx5: port 1 MAC address is e4:1d:2d:e7:0c:fa
    EAL: PCI device 0000:06:00.1 on NUMA socket 0
    EAL:   probe driver: 15b3:1013 librte_pmd_mlx5
    PMD: librte_pmd_mlx5: PCI information matches, using device "mlx5_3" (VF: false)
    PMD: librte_pmd_mlx5: 1 port(s) detected
    PMD: librte_pmd_mlx5: port 1 MAC address is e4:1d:2d:e7:0c:fb
    Interactive-mode selected
    Configuring Port 0 (socket 0)
    PMD: librte_pmd_mlx5: 0x8cba80: TX queues number update: 0 -> 2
    PMD: librte_pmd_mlx5: 0x8cba80: RX queues number update: 0 -> 2
    Port 0: E4:1D:2D:E7:0C:FE
    Configuring Port 1 (socket 0)
    PMD: librte_pmd_mlx5: 0x8ccac8: TX queues number update: 0 -> 2
    PMD: librte_pmd_mlx5: 0x8ccac8: RX queues number update: 0 -> 2
    Port 1: E4:1D:2D:E7:0C:FF
    Configuring Port 2 (socket 0)
    PMD: librte_pmd_mlx5: 0x8cdb10: TX queues number update: 0 -> 2
    PMD: librte_pmd_mlx5: 0x8cdb10: RX queues number update: 0 -> 2
    Port 2: E4:1D:2D:E7:0C:FA
    Configuring Port 3 (socket 0)
    PMD: librte_pmd_mlx5: 0x8ceb58: TX queues number update: 0 -> 2
    PMD: librte_pmd_mlx5: 0x8ceb58: RX queues number update: 0 -> 2
    Port 3: E4:1D:2D:E7:0C:FB
    Checking link statuses...
    Port 0 Link Up - speed 40000 Mbps - full-duplex
    Port 1 Link Up - speed 40000 Mbps - full-duplex
    Port 2 Link Up - speed 10000 Mbps - full-duplex
    Port 3 Link Up - speed 10000 Mbps - full-duplex