23. MLX4 poll mode driver library

23.1. 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.

23.2. Configuration

23.3. Limitations

• CRC stripping is supported by default and always reported as “true”. The ability to enable/disable CRC stripping requires OFED version 4.3-1.5.0.0 and above or rdma-core version v18 and above.

23.4. 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 (provided by rdma-core package)

  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 (provided by rdma-core package)

  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

  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.

Depending on system constraints and user preferences either RDMA core library with a recent enough Linux kernel release (recommended) or Mellanox OFED, which provides compatibility with older releases.

23.5. Supported NICs

• Mellanox(R) ConnectX(R)-3 Pro 40G MCX354A-FCC_Ax (2*40G)

23.6. Quick Start Guide

1. Set all ports links to Ethernet

   PCI=<NIC PCI address>
   echo eth > "/sys/bus/pci/devices/$PCI/mlx4_port0"
   echo eth > "/sys/bus/pci/devices/$PCI/mlx4_port1"
   

   Note

   If using Mellanox OFED one can permanently set the port link to Ethernet using connectx_port_config tool provided by it. Mellanox OFED as a fallback:

2. In case of bare metal or hypervisor, configure optimized steering mode by adding the following line to /etc/modprobe.d/mlx4_core.conf:

   options mlx4_core log_num_mgm_entry_size=-7
   

   Note

   If VLAN filtering is used, set log_num_mgm_entry_size=-1. Performance degradation can occur on this case.

3. Restart the driver:

   /etc/init.d/openibd restart
   

   or:

   service openibd restart
   

4. Compile DPDK and you are ready to go. See instructions on Development Kit Build System

23.7. Performance tuning

1. Verify the optimized steering mode is configured:

cat /sys/module/mlx4_core/parameters/log_num_mgm_entry_size

2. Use the CPU near local NUMA node to which the PCIe adapter is connected, for better performance. For VMs, verify that the right CPU and NUMA node are pinned according to the above. Run:

   lstopo-no-graphics
   

   to identify the NUMA node to which the PCIe adapter is connected.

3. If more than one adapter is used, and root complex capabilities allow to put both adapters on the same NUMA node without PCI bandwidth degradation, it is recommended to locate both adapters on the same NUMA node. This in order to forward packets from one to the other without NUMA performance penalty.

4. Disable pause frames:

   ethtool -A <netdev> rx off tx off
   

5. Verify IO non-posted prefetch is disabled by default. This can be checked via the BIOS configuration. Please contact you server provider for more information about the settings.

setpci -s <NIC PCI address> 68.w

setpci -s <NIC PCI address> 68.w=3XXX

6. To minimize overhead of searching Memory Regions:
   • ‘–socket-mem’ is recommended to pin memory by predictable amount.
   • Configure per-lcore cache when creating Mempools for packet buffer.
   • Refrain from dynamically allocating/freeing memory in run-time.

23.8. 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 -l 8-15 -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>