12. MLX4 poll mode driver library

12.1. Implementation details

Most Mellanox ConnectX-3 devices provide two ports but expose a single PCI bus address, thus unlike most drivers, librte_pmd_mlx4 registers itself as a PCI driver that allocates one Ethernet device per detected port.

For this reason, one cannot white/blacklist a single port without also white/blacklisting the others on the same device.

Besides its dependency on libibverbs (that implies libmlx4 and associated kernel support), librte_pmd_mlx4 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.

Compiling librte_pmd_mlx4 causes DPDK to be linked against libibverbs.

12.2. Features

• RSS, also known as RCA, is supported. In this mode the number of configured RX queues must be a power of two.
• VLAN filtering is supported.
• Link state information is provided.
• Promiscuous mode is supported.
• All multicast mode is supported.
• Multiple MAC addresses (unicast, multicast) can be configured.
• Scattered packets are supported for TX and RX.
• Inner L3/L4 (IP, TCP and UDP) TX/RX checksum offloading and validation.
• Outer L3 (IP) TX/RX checksum offloading and validation for VXLAN frames.
• Secondary process TX is supported.

12.3. Limitations

• RSS hash key cannot be modified.
• RSS RETA cannot be configured
• RSS always includes L3 (IPv4/IPv6) and L4 (UDP/TCP). They cannot be dissociated.
• Hardware counters are not implemented (they are software counters).
• Secondary process RX is not supported.

12.4. Configuration

12.5. 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_mlx4. This library provides a generic interface between the kernel and low-level user space drivers such as libmlx4.

  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.

• libmlx4

  Low-level user space driver library for Mellanox ConnectX-3 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:

  • mlx4_core: hardware driver managing Mellanox ConnectX-3 devices.
  • mlx4_en: Ethernet device driver that provides kernel network interfaces.
  • mlx4_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-3 adapters.

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

Currently supported by DPDK:

• Mellanox OFED 3.1.
• Firmware version 2.35.5100 and higher.
• Supported architectures: x86_64 and POWER8.

12.6. Usage example

This section demonstrates how to launch testpmd with Mellanox ConnectX-3 devices managed by librte_pmd_mlx4.

1. Load the kernel modules:

   modprobe -a ib_uverbs mlx4_en mlx4_core mlx4_ib
   

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

   /etc/init.d/openibd restart
   

   Note

   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:

   eth2
   eth3
   eth4
   eth5
   

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

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

   Example output:

   -w 0000:83:00.0
   -w 0000:83:00.0
   -w 0000:84:00.0
   -w 0000:84:00.0
   

   Note

   There are only two distinct PCI bus addresses because the Mellanox ConnectX-3 adapters installed on this system are dual port.

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 0000:83:00.0 -w 0000:84:00.0 -- --rxq=2 --txq=2 -i
   

   Example output:

   [...]
   EAL: PCI device 0000:83:00.0 on NUMA socket 1
   EAL:   probe driver: 15b3:1007 librte_pmd_mlx4
   PMD: librte_pmd_mlx4: PCI information matches, using device "mlx4_0" (VF: false)
   PMD: librte_pmd_mlx4: 2 port(s) detected
   PMD: librte_pmd_mlx4: port 1 MAC address is 00:02:c9:b5:b7:50
   PMD: librte_pmd_mlx4: port 2 MAC address is 00:02:c9:b5:b7:51
   EAL: PCI device 0000:84:00.0 on NUMA socket 1
   EAL:   probe driver: 15b3:1007 librte_pmd_mlx4
   PMD: librte_pmd_mlx4: PCI information matches, using device "mlx4_1" (VF: false)
   PMD: librte_pmd_mlx4: 2 port(s) detected
   PMD: librte_pmd_mlx4: port 1 MAC address is 00:02:c9:b5:ba:b0
   PMD: librte_pmd_mlx4: port 2 MAC address is 00:02:c9:b5:ba:b1
   Interactive-mode selected
   Configuring Port 0 (socket 0)
   PMD: librte_pmd_mlx4: 0x867d60: TX queues number update: 0 -> 2
   PMD: librte_pmd_mlx4: 0x867d60: RX queues number update: 0 -> 2
   Port 0: 00:02:C9:B5:B7:50
   Configuring Port 1 (socket 0)
   PMD: librte_pmd_mlx4: 0x867da0: TX queues number update: 0 -> 2
   PMD: librte_pmd_mlx4: 0x867da0: RX queues number update: 0 -> 2
   Port 1: 00:02:C9:B5:B7:51
   Configuring Port 2 (socket 0)
   PMD: librte_pmd_mlx4: 0x867de0: TX queues number update: 0 -> 2
   PMD: librte_pmd_mlx4: 0x867de0: RX queues number update: 0 -> 2
   Port 2: 00:02:C9:B5:BA:B0
   Configuring Port 3 (socket 0)
   PMD: librte_pmd_mlx4: 0x867e20: TX queues number update: 0 -> 2
   PMD: librte_pmd_mlx4: 0x867e20: RX queues number update: 0 -> 2
   Port 3: 00:02:C9:B5:BA:B1
   Checking link statuses...
   Port 0 Link Up - speed 10000 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 40000 Mbps - full-duplex
   Done
   testpmd>