10. ENA Poll Mode Driver

The ENA PMD is a DPDK poll-mode driver for the Amazon Elastic Network Adapter (ENA) family.

10.1. Overview

The ENA driver exposes a lightweight management interface with a minimal set of memory mapped registers and an extendable command set through an Admin Queue.

The driver supports a wide range of ENA adapters, is link-speed independent (i.e., the same driver is used for 10GbE, 25GbE, 40GbE, etc.), and it negotiates and supports an extendable feature set.

ENA adapters allow high speed and low overhead Ethernet traffic processing by providing a dedicated Tx/Rx queue pair per CPU core.

The ENA driver supports industry standard TCP/IP offload features such as checksum offload and TCP transmit segmentation offload (TSO).

Receive-side scaling (RSS) is supported for multi-core scaling.

Some of the ENA devices support a working mode called Low-latency Queue (LLQ), which saves several more microseconds.

10.2. Management Interface

ENA management interface is exposed by means of:

  • Device Registers
  • Admin Queue (AQ) and Admin Completion Queue (ACQ)

ENA device memory-mapped PCIe space for registers (MMIO registers) are accessed only during driver initialization and are not involved in further normal device operation.

AQ is used for submitting management commands, and the results/responses are reported asynchronously through ACQ.

ENA introduces a very small set of management commands with room for vendor-specific extensions. Most of the management operations are framed in a generic Get/Set feature command.

The following admin queue commands are supported:

  • Create I/O submission queue
  • Create I/O completion queue
  • Destroy I/O submission queue
  • Destroy I/O completion queue
  • Get feature
  • Set feature
  • Get statistics

Refer to ena_admin_defs.h for the list of supported Get/Set Feature properties.

10.3. Data Path Interface

I/O operations are based on Tx and Rx Submission Queues (Tx SQ and Rx SQ correspondingly). Each SQ has a completion queue (CQ) associated with it.

The SQs and CQs are implemented as descriptor rings in contiguous physical memory.

Refer to ena_eth_io_defs.h for the detailed structure of the descriptor

The driver supports multi-queue for both Tx and Rx.

10.4. Configuration information

DPDK Configuration Parameters

The following configuration options are available for the ENA PMD:

  • CONFIG_RTE_LIBRTE_ENA_PMD (default y): Enables or disables inclusion of the ENA PMD driver in the DPDK compilation.
  • CONFIG_RTE_LIBRTE_ENA_DEBUG_INIT (default y): Enables or disables debug logging of device initialization within the ENA PMD driver.
  • CONFIG_RTE_LIBRTE_ENA_DEBUG_RX (default n): Enables or disables debug logging of RX logic within the ENA PMD driver.
  • CONFIG_RTE_LIBRTE_ENA_DEBUG_TX (default n): Enables or disables debug logging of TX logic within the ENA PMD driver.
  • CONFIG_RTE_LIBRTE_ENA_COM_DEBUG (default n): Enables or disables debug logging of low level tx/rx logic in ena_com(base) within the ENA PMD driver.

ENA Configuration Parameters

  • Number of Queues

    This is the requested number of queues upon initialization, however, the actual number of receive and transmit queues to be created will be the minimum between the maximal number supported by the device and number of queues requested.

  • Size of Queues

    This is the requested size of receive/transmit queues, while the actual size will be the minimum between the requested size and the maximal receive/transmit supported by the device.

10.5. Building DPDK

See the DPDK Getting Started Guide for Linux for instructions on how to build DPDK.

By default the ENA PMD library will be built into the DPDK library.

For configuring and using UIO and VFIO frameworks, please also refer the documentation that comes with DPDK suite.

10.6. Supported ENA adapters

Current ENA PMD supports the following ENA adapters including:

  • 1d0f:ec20 - ENA VF
  • 1d0f:ec21 - ENA VF with LLQ support

10.7. Supported Operating Systems

Any Linux distribution fulfilling the conditions described in System Requirements section of the DPDK documentation or refer to DPDK Release Notes.

10.8. Supported features

  • Jumbo frames up to 9K
  • Port Hardware Statistics
  • IPv4/TCP/UDP checksum offload
  • TSO offload
  • Multiple receive and transmit queues
  • RSS
  • Low Latency Queue for Tx

10.9. Unsupported features

The features supported by the device and not yet supported by this PMD include:

  • Asynchronous Event Notification Queue (AENQ)

10.10. Prerequisites

  1. Prepare the system as recommended by DPDK suite. This includes environment variables, hugepages configuration, tool-chains and configuration
  2. Insert igb_uio kernel module using the command ‘modprobe igb_uio’
  3. Bind the intended ENA device to igb_uio module

At this point the system should be ready to run DPDK applications. Once the application runs to completion, the ENA can be detached from igb_uio if necessary.

10.11. Usage example

Follow instructions available in the document compiling and testing a PMD for a NIC to launch testpmd with Amazon ENA devices managed by librte_pmd_ena.

Example output:

[...]
EAL: PCI device 0000:02:00.1 on NUMA socket -1
EAL:   probe driver: 1d0f:ec20 rte_ena_pmd
EAL:   PCI memory mapped at 0x7f9b6c400000
PMD: eth_ena_dev_init(): Initializing 0:2:0.1
Interactive-mode selected
Configuring Port 0 (socket 0)
Port 0: 00:00:00:11:00:01
Checking link statuses...
Port 0 Link Up - speed 10000 Mbps - full-duplex
Done
testpmd>