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Diffstat (limited to 'Documentation/networking/device_drivers/ethernet/amazon/ena.rst')
| -rw-r--r-- | Documentation/networking/device_drivers/ethernet/amazon/ena.rst | 164 |
1 files changed, 78 insertions, 86 deletions
diff --git a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst index f8c6469f2bd2..01b2a69b0cb0 100644 --- a/Documentation/networking/device_drivers/ethernet/amazon/ena.rst +++ b/Documentation/networking/device_drivers/ethernet/amazon/ena.rst @@ -11,12 +11,12 @@ 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 +minimal set of memory mapped registers and extendible 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. +(i.e., the same driver is used for 10GbE, 25GbE, 40GbE, etc), and has +a negotiated and extendible 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. @@ -27,9 +27,9 @@ 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 supports industry standard TCP/IP offload features such as +checksum offload. 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 @@ -38,22 +38,20 @@ debug logs. Some of the ENA devices support a working mode called Low-latency Queue (LLQ), which saves several more microseconds. - 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. + 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. ================= ====================================================== @@ -69,7 +67,7 @@ ENA management interface is exposed by means of: - Asynchronous Event Notification Queue (AENQ) ENA device MMIO Registers are accessed only during driver -initialization and are not involved in further normal device +initialization and are not used during further normal device operation. AQ is used for submitting management commands, and the @@ -100,28 +98,27 @@ 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** - ==================== =============== +==================== =============== +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. +Keep-Alive is a special mechanism that allows monitoring the device's health. +A Keep-Alive event is delivered by the device every second. +The driver maintains a watchdog (WD) handler which logs the current state and +statistics. If the keep-alive events aren't delivered as expected the WD resets +the device and the driver. 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. @@ -131,26 +128,24 @@ physical memory. The ENA driver supports two Queue Operation modes for Tx SQs: -- Regular mode +- **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. - * 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. -- 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. + **Note that** 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 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: @@ -165,6 +160,7 @@ benefits: 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). @@ -190,20 +186,21 @@ 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 +**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 +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 +**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. -Adaptive coalescing can be switched on/off through ethtool(8) -adaptive_rx on|off parameter. +Adaptive coalescing can be switched on/off through `ethtool(8)`'s +:code:`adaptive_rx on|off` parameter. More information about Adaptive Interrupt Moderation (DIM) can be found in Documentation/networking/net_dim.rst @@ -214,17 +211,10 @@ 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 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. @@ -232,22 +222,23 @@ 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. +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. @@ -260,41 +251,42 @@ RSS 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). + indirection table through `ethtool(8)`. DATA PATH ========= + Tx -- -ena_start_xmit() is called by the stack. This function does the following: +:code:`ena_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.) +- 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 +- 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. + 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.) +- Calls :code:`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.) + to the Device memory space (if in push mode). -- Writes doorbell to the ENA device. +- Writes a 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 +- The :code:`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. + * ``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. @@ -303,12 +295,11 @@ 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 +- The :code:`ena_clean_rx_irq()` function is called. This function calls + :code:`ena_com_rx_pkt()`, an ENA communication layer function, which returns the + number of descriptors used for a new 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: +- :code:`ena_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 @@ -317,9 +308,10 @@ Rx - 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. + * Otherwise the function unmaps the Rx buffer, sets the first + descriptor as `skb`'s linear part and the other descriptors as the + `skb`'s 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(). + checksum hw verify result, etc), and then passed to the network + stack, using the NAPI interface function :code:`napi_gro_receive()`. |