16. ENA Poll Mode Driver
The ENA PMD is a DPDK poll-mode driver for the Amazon Elastic Network Adapter (ENA) family.
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.
16.2. 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
ena_admin_defs.h for the list of supported Get/Set Feature
16.3. 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.
ena_eth_io_defs.h for the detailed structure of the descriptor
The driver supports multi-queue for both Tx and Rx.
16.4. 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_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.
16.5. 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.
16.6. Supported ENA adapters
Current ENA PMD supports the following ENA adapters including:
1d0f:ec20- ENA VF
1d0f:ec21- ENA VF with LLQ support
16.7. Supported Operating Systems
Any Linux distribution fulfilling the conditions described in
section of the DPDK documentation or refer to DPDK Release Notes.
16.8. Supported features
- MTU configuration
- Jumbo frames up to 9K
- IPv4/TCP/UDP checksum offload
- TSO offload
- Multiple receive and transmit queues
- RSS hash
- RSS indirection table configuration
- Low Latency Queue for Tx
- Basic and extended statistics
- LSC event notification
- Watchdog (requires handling of timers in the application)
- Device reset upon failure
Prepare the system as recommended by DPDK suite. This includes environment variables, hugepages configuration, tool-chains and configuration.
ENA PMD can operate with
vfio-pci``(*) or ``igb_uiodriver.
(*) ENAv2 hardware supports Low Latency Queue v2 (LLQv2). This feature reduces the latency of the packets by pushing the header directly through the PCI to the device, before the DMA is even triggered. For proper work kernel PCI driver must support write combining (WC). In mainline version of
igb_uio(in DPDK repo) it must be enabled by loading module with
wc_activate=1flag (example below). However, mainline’s vfio-pci driver in kernel doesn’t have WC support yet (planed to be added). If vfio-pci used user should be either turn off ENAv2 (to avoid performance impact) or recompile vfio-pci driver with patch provided in amzn-github.
igb_uiokernel module using the command
modprobe uio; insmod igb_uio.ko wc_activate=1respectively.
vfio-pciusers only: Please make sure that
IOMMUis enabled in your system, or use
echo 1 > /sys/module/vfio/parameters/enable_unsafe_noiommu_mode
Bind the intended ENA device to
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.
16.10. 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.
[...] EAL: PCI device 0000:00:06.0 on NUMA socket -1 EAL: Invalid NUMA socket, default to 0 EAL: probe driver: 1d0f:ec20 net_ena Interactive-mode selected testpmd: create a new mbuf pool <mbuf_pool_socket_0>: n=171456, size=2176, socket=0 testpmd: preferred mempool ops selected: ring_mp_mc Warning! port-topology=paired and odd forward ports number, the last port will pair with itself. Configuring Port 0 (socket 0) Port 0: 00:00:00:11:00:01 Checking link statuses... Done testpmd>