309 lines
12 KiB
Plaintext
309 lines
12 KiB
Plaintext
|
Linux kernel driver for Elastic Network Adapter (ENA) family:
|
||
|
|
=============================================================
|
||
|
|
|
||
|
|
Overview:
|
||
|
|
=========
|
||
|
|
ENA is a networking interface designed to make good use of modern CPU
|
||
|
|
features and system architectures.
|
||
|
|
|
||
|
|
The ENA device exposes a lightweight management interface with a
|
||
|
|
minimal set of memory mapped registers and extendable command set
|
||
|
|
through an Admin Queue.
|
||
|
|
|
||
|
|
The driver supports a range of ENA devices, is link-speed independent
|
||
|
|
(i.e., the same driver is used for 10GbE, 25GbE, 40GbE, etc.), and has
|
||
|
|
a negotiated and extendable feature set.
|
||
|
|
|
||
|
|
Some ENA devices support SR-IOV. This driver is used for both the
|
||
|
|
SR-IOV Physical Function (PF) and Virtual Function (VF) devices.
|
||
|
|
|
||
|
|
ENA devices enable high speed and low overhead network traffic
|
||
|
|
processing by providing multiple Tx/Rx queue pairs (the maximum number
|
||
|
|
is advertised by the device via the Admin Queue), a dedicated MSI-X
|
||
|
|
interrupt vector per Tx/Rx queue pair, adaptive interrupt moderation,
|
||
|
|
and CPU cacheline optimized data placement.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
The ENA driver and its corresponding devices implement health
|
||
|
|
monitoring mechanisms such as watchdog, enabling the device and driver
|
||
|
|
to recover in a manner transparent to the application, as well as
|
||
|
|
debug logs.
|
||
|
|
|
||
|
|
Some of the ENA devices support a working mode called Low-latency
|
||
|
|
Queue (LLQ), which saves several more microseconds.
|
||
|
|
|
||
|
|
Supported PCI vendor ID/device IDs:
|
||
|
|
===================================
|
||
|
|
1d0f:0ec2 - ENA PF
|
||
|
|
1d0f:1ec2 - ENA PF with LLQ support
|
||
|
|
1d0f:ec20 - ENA VF
|
||
|
|
1d0f:ec21 - ENA VF with LLQ support
|
||
|
|
|
||
|
|
ENA Source Code Directory Structure:
|
||
|
|
====================================
|
||
|
|
ena_com.[ch] - Management communication layer. This layer is
|
||
|
|
responsible for the handling all the management
|
||
|
|
(admin) communication between the device and the
|
||
|
|
driver.
|
||
|
|
ena_eth_com.[ch] - Tx/Rx data path.
|
||
|
|
ena_admin_defs.h - Definition of ENA management interface.
|
||
|
|
ena_eth_io_defs.h - Definition of ENA data path interface.
|
||
|
|
ena_common_defs.h - Common definitions for ena_com layer.
|
||
|
|
ena_regs_defs.h - Definition of ENA PCI memory-mapped (MMIO) registers.
|
||
|
|
ena_netdev.[ch] - Main Linux kernel driver.
|
||
|
|
ena_syfsfs.[ch] - Sysfs files.
|
||
|
|
ena_ethtool.c - ethtool callbacks.
|
||
|
|
ena_pci_id_tbl.h - Supported device IDs.
|
||
|
|
|
||
|
|
Management Interface:
|
||
|
|
=====================
|
||
|
|
ENA management interface is exposed by means of:
|
||
|
|
- PCIe Configuration Space
|
||
|
|
- Device Registers
|
||
|
|
- Admin Queue (AQ) and Admin Completion Queue (ACQ)
|
||
|
|
- Asynchronous Event Notification Queue (AENQ)
|
||
|
|
|
||
|
|
ENA device 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 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
|
||
|
|
- Configure AENQ
|
||
|
|
- Get statistics
|
||
|
|
|
||
|
|
Refer to ena_admin_defs.h for the list of supported Get/Set Feature
|
||
|
|
properties.
|
||
|
|
|
||
|
|
The Asynchronous Event Notification Queue (AENQ) is a uni-directional
|
||
|
|
queue used by the ENA device to send to the driver events that cannot
|
||
|
|
be reported using ACQ. AENQ events are subdivided into groups. Each
|
||
|
|
group may have multiple syndromes, as shown below
|
||
|
|
|
||
|
|
The events are:
|
||
|
|
Group Syndrome
|
||
|
|
Link state change - X -
|
||
|
|
Fatal error - X -
|
||
|
|
Notification Suspend traffic
|
||
|
|
Notification Resume traffic
|
||
|
|
Keep-Alive - X -
|
||
|
|
|
||
|
|
ACQ and AENQ share the same MSI-X vector.
|
||
|
|
|
||
|
|
Keep-Alive is a special mechanism that allows monitoring of the
|
||
|
|
device's health. The driver maintains a watchdog (WD) handler which,
|
||
|
|
if fired, logs the current state and statistics then resets and
|
||
|
|
restarts the ENA device and driver. A Keep-Alive event is delivered by
|
||
|
|
the device every second. The driver re-arms the WD upon reception of a
|
||
|
|
Keep-Alive event. A missed Keep-Alive event causes the WD handler to
|
||
|
|
fire.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
The ENA driver supports two Queue Operation modes for Tx SQs:
|
||
|
|
- Regular mode
|
||
|
|
* In this mode the Tx SQs reside in the host's memory. The ENA
|
||
|
|
device fetches the ENA Tx descriptors and packet data from host
|
||
|
|
memory.
|
||
|
|
- Low Latency Queue (LLQ) mode or "push-mode".
|
||
|
|
* In this mode the driver pushes the transmit descriptors and the
|
||
|
|
first 128 bytes of the packet directly to the ENA device memory
|
||
|
|
space. The rest of the packet payload is fetched by the
|
||
|
|
device. For this operation mode, the driver uses a dedicated PCI
|
||
|
|
device memory BAR, which is mapped with write-combine capability.
|
||
|
|
|
||
|
|
The Rx SQs support only the regular mode.
|
||
|
|
|
||
|
|
Note: Not all ENA devices support LLQ, and this feature is negotiated
|
||
|
|
with the device upon initialization. If the ENA device does not
|
||
|
|
support LLQ mode, the driver falls back to the regular mode.
|
||
|
|
|
||
|
|
The driver supports multi-queue for both Tx and Rx. This has various
|
||
|
|
benefits:
|
||
|
|
- Reduced CPU/thread/process contention on a given Ethernet interface.
|
||
|
|
- Cache miss rate on completion is reduced, particularly for data
|
||
|
|
cache lines that hold the sk_buff structures.
|
||
|
|
- Increased process-level parallelism when handling received packets.
|
||
|
|
- Increased data cache hit rate, by steering kernel processing of
|
||
|
|
packets to the CPU, where the application thread consuming the
|
||
|
|
packet is running.
|
||
|
|
- In hardware interrupt re-direction.
|
||
|
|
|
||
|
|
Interrupt Modes:
|
||
|
|
================
|
||
|
|
The driver assigns a single MSI-X vector per queue pair (for both Tx
|
||
|
|
and Rx directions). The driver assigns an additional dedicated MSI-X vector
|
||
|
|
for management (for ACQ and AENQ).
|
||
|
|
|
||
|
|
Management interrupt registration is performed when the Linux kernel
|
||
|
|
probes the adapter, and it is de-registered when the adapter is
|
||
|
|
removed. I/O queue interrupt registration is performed when the Linux
|
||
|
|
interface of the adapter is opened, and it is de-registered when the
|
||
|
|
interface is closed.
|
||
|
|
|
||
|
|
The management interrupt is named:
|
||
|
|
ena-mgmnt@pci:<PCI domain:bus:slot.function>
|
||
|
|
and for each queue pair, an interrupt is named:
|
||
|
|
<interface name>-Tx-Rx-<queue index>
|
||
|
|
|
||
|
|
The ENA device operates in auto-mask and auto-clear interrupt
|
||
|
|
modes. That is, once MSI-X is delivered to the host, its Cause bit is
|
||
|
|
automatically cleared and the interrupt is masked. The interrupt is
|
||
|
|
unmasked by the driver after NAPI processing is complete.
|
||
|
|
|
||
|
|
Interrupt Moderation:
|
||
|
|
=====================
|
||
|
|
ENA driver and device can operate in conventional or adaptive interrupt
|
||
|
|
moderation mode.
|
||
|
|
|
||
|
|
In conventional mode the driver instructs device to postpone interrupt
|
||
|
|
posting according to static interrupt delay value. The interrupt delay
|
||
|
|
value can be configured through ethtool(8). The following ethtool
|
||
|
|
parameters are supported by the driver: tx-usecs, rx-usecs
|
||
|
|
|
||
|
|
In adaptive interrupt moderation mode the interrupt delay value is
|
||
|
|
updated by the driver dynamically and adjusted every NAPI cycle
|
||
|
|
according to the traffic nature.
|
||
|
|
|
||
|
|
By default ENA driver applies adaptive coalescing on Rx traffic and
|
||
|
|
conventional coalescing on Tx traffic.
|
||
|
|
|
||
|
|
Adaptive coalescing can be switched on/off through ethtool(8)
|
||
|
|
adaptive_rx on|off parameter.
|
||
|
|
|
||
|
|
The driver chooses interrupt delay value according to the number of
|
||
|
|
bytes and packets received between interrupt unmasking and interrupt
|
||
|
|
posting. The driver uses interrupt delay table that subdivides the
|
||
|
|
range of received bytes/packets into 5 levels and assigns interrupt
|
||
|
|
delay value to each level.
|
||
|
|
|
||
|
|
The user can enable/disable adaptive moderation, modify the interrupt
|
||
|
|
delay table and restore its default values through sysfs.
|
||
|
|
|
||
|
|
RX copybreak:
|
||
|
|
=============
|
||
|
|
The rx_copybreak is initialized by default to ENA_DEFAULT_RX_COPYBREAK
|
||
|
|
and can be configured by the ETHTOOL_STUNABLE command of the
|
||
|
|
SIOCETHTOOL ioctl.
|
||
|
|
|
||
|
|
SKB:
|
||
|
|
====
|
||
|
|
The driver-allocated SKB for frames received from Rx handling using
|
||
|
|
NAPI context. The allocation method depends on the size of the packet.
|
||
|
|
If the frame length is larger than rx_copybreak, napi_get_frags()
|
||
|
|
is used, otherwise netdev_alloc_skb_ip_align() is used, the buffer
|
||
|
|
content is copied (by CPU) to the SKB, and the buffer is recycled.
|
||
|
|
|
||
|
|
Statistics:
|
||
|
|
===========
|
||
|
|
The user can obtain ENA device and driver statistics using ethtool.
|
||
|
|
The driver can collect regular or extended statistics (including
|
||
|
|
per-queue stats) from the device.
|
||
|
|
|
||
|
|
In addition the driver logs the stats to syslog upon device reset.
|
||
|
|
|
||
|
|
MTU:
|
||
|
|
====
|
||
|
|
The driver supports an arbitrarily large MTU with a maximum that is
|
||
|
|
negotiated with the device. The driver configures MTU using the
|
||
|
|
SetFeature command (ENA_ADMIN_MTU property). The user can change MTU
|
||
|
|
via ip(8) and similar legacy tools.
|
||
|
|
|
||
|
|
Stateless Offloads:
|
||
|
|
===================
|
||
|
|
The ENA driver supports:
|
||
|
|
- TSO over IPv4/IPv6
|
||
|
|
- TSO with ECN
|
||
|
|
- IPv4 header checksum offload
|
||
|
|
- TCP/UDP over IPv4/IPv6 checksum offloads
|
||
|
|
|
||
|
|
RSS:
|
||
|
|
====
|
||
|
|
- The ENA device supports RSS that allows flexible Rx traffic
|
||
|
|
steering.
|
||
|
|
- Toeplitz and CRC32 hash functions are supported.
|
||
|
|
- Different combinations of L2/L3/L4 fields can be configured as
|
||
|
|
inputs for hash functions.
|
||
|
|
- The driver configures RSS settings using the AQ SetFeature command
|
||
|
|
(ENA_ADMIN_RSS_HASH_FUNCTION, ENA_ADMIN_RSS_HASH_INPUT and
|
||
|
|
ENA_ADMIN_RSS_REDIRECTION_TABLE_CONFIG properties).
|
||
|
|
- If the NETIF_F_RXHASH flag is set, the 32-bit result of the hash
|
||
|
|
function delivered in the Rx CQ descriptor is set in the received
|
||
|
|
SKB.
|
||
|
|
- The user can provide a hash key, hash function, and configure the
|
||
|
|
indirection table through ethtool(8).
|
||
|
|
|
||
|
|
DATA PATH:
|
||
|
|
==========
|
||
|
|
Tx:
|
||
|
|
---
|
||
|
|
end_start_xmit() is called by the stack. This function does the following:
|
||
|
|
- Maps data buffers (skb->data and frags).
|
||
|
|
- Populates ena_buf for the push buffer (if the driver and device are
|
||
|
|
in push mode.)
|
||
|
|
- Prepares ENA bufs for the remaining frags.
|
||
|
|
- Allocates a new request ID from the empty req_id ring. The request
|
||
|
|
ID is the index of the packet in the Tx info. This is used for
|
||
|
|
out-of-order TX completions.
|
||
|
|
- Adds the packet to the proper place in the Tx ring.
|
||
|
|
- Calls ena_com_prepare_tx(), an ENA communication layer that converts
|
||
|
|
the ena_bufs to ENA descriptors (and adds meta ENA descriptors as
|
||
|
|
needed.)
|
||
|
|
* This function also copies the ENA descriptors and the push buffer
|
||
|
|
to the Device memory space (if in push mode.)
|
||
|
|
- Writes doorbell to the ENA device.
|
||
|
|
- When the ENA device finishes sending the packet, a completion
|
||
|
|
interrupt is raised.
|
||
|
|
- The interrupt handler schedules NAPI.
|
||
|
|
- The ena_clean_tx_irq() function is called. This function handles the
|
||
|
|
completion descriptors generated by the ENA, with a single
|
||
|
|
completion descriptor per completed packet.
|
||
|
|
* req_id is retrieved from the completion descriptor. The tx_info of
|
||
|
|
the packet is retrieved via the req_id. The data buffers are
|
||
|
|
unmapped and req_id is returned to the empty req_id ring.
|
||
|
|
* The function stops when the completion descriptors are completed or
|
||
|
|
the budget is reached.
|
||
|
|
|
||
|
|
Rx:
|
||
|
|
---
|
||
|
|
- When a packet is received from the ENA device.
|
||
|
|
- The interrupt handler schedules NAPI.
|
||
|
|
- The ena_clean_rx_irq() function is called. This function calls
|
||
|
|
ena_rx_pkt(), an ENA communication layer function, which returns the
|
||
|
|
number of descriptors used for a new unhandled packet, and zero if
|
||
|
|
no new packet is found.
|
||
|
|
- Then it calls the ena_clean_rx_irq() function.
|
||
|
|
- ena_eth_rx_skb() checks packet length:
|
||
|
|
* If the packet is small (len < rx_copybreak), the driver allocates
|
||
|
|
a SKB for the new packet, and copies the packet payload into the
|
||
|
|
SKB data buffer.
|
||
|
|
- In this way the original data buffer is not passed to the stack
|
||
|
|
and is reused for future Rx packets.
|
||
|
|
* Otherwise the function unmaps the Rx buffer, then allocates the
|
||
|
|
new SKB structure and hooks the Rx buffer to the SKB frags.
|
||
|
|
- The new SKB is updated with the necessary information (protocol,
|
||
|
|
checksum hw verify result, etc.), and then passed to the network
|
||
|
|
stack, using the NAPI interface function napi_gro_receive().
|