DPA Subsystem

DOCA SDK 2.6.0

The NVIDIA® BlueField®-3 data-path accelerator (DPA) is an embedded subsystem designed to accelerate workloads that require high-performance access to the NIC engines in certain packet and I/O processing workloads. Applications leveraging DPA capabilities run faster on the DPA than on host. Unlike other programmable embedded technologies, such as FPGAs, the DPA enables a high degree of programmability using the C programming model, multi-process support, tools chains like compilers and debuggers, SDKs, dynamic application loading, and management.

The DPA architecture is optimized for executing packet and I/O processing workloads. As such, the DPA subsystem is characterized by having many execution units that can work in parallel to overcome latency issues (such as access to host memory) and provide an overall higher throughput.

The following diagram illustrates the DPA subsystem. The application accesses the DPA through the DOCA library (DOCA DPA) or the DOCA driver layer (FlexIO SDK). On the host or DPU side, the application loads its code into the DPA (shown as "Running DPA Process") as well as allocates memory, NIC queues, and more resources for the DPA process to access. The DPA process can use device side libraries to access the resources. The provided APIs support signaling of the DPA process from the host or DPU to explicitly pass control or to obtain results from the DPA.

dpa-platform-version-1-modificationdate-1704292972197-api-v2.png

The threads on the DPA can react independently to incoming messages via interrupts from the hardware, thereby providing full bypass of DPU or Arm CPU for datapath operations.

The following sections provide an overview of the DPA platform design.

The DPA platform supports multiple processes with each process having multiple threads. Each thread can be mapped to a different execution unit to achieve parallel execution. The processes operate within their own address spaces and their execution contexts are isolated. Processes are loaded and unloaded dynamically per the user's request. This is achieved by the platform's hardware design (i.e., privilege layers, memory translation units, DMA engines) and a light-weight real-time operating system (RTOS). The RTOS enforces the privileges and isolation among the different processes.

The RTOS is designed to rely on hardware-based scheduling to enable low activation latency for the execution handlers. The RTOS works in a cooperative run-to-completion scheduling model.

Under cooperative scheduling, an execution handler can use the execution unit without interrupts until it relinquishes it. Once relinquished, the execution unit is handed back to the RTOS to schedule the next handler. The RTOS sets a watchdog for the handlers to prevent any handler from unduly monopolizing the execution units.

The following diagram illustrates the DPA memory hierarchy. Memory accessed by the DPA can be cached at three levels (L1, L2, and L3). Each execution unit has a private L1 data cache. The L1 code cache is shared among all the execution units in a DPA core. The L2 cache is shared among all the DPA cores. The DPA execution units can access external memory via load/store operations through the Memory Apertures.

The external memory that is fetched can be cached directly in L1. The DPA caches are backed by NIC private memory, which is located in the DPU's DDR memory banks. Therefore, the address spaces are scalable and bound only by the size of the NIC's private memory, which in turn is limited only by the DPU's DDR capacity.

dpa-memory-hierarchy-diagram-version-1-modificationdate-1704292970253-api-v2.png

See " Memory Model " for more details.

The DPA can send and receive any kind of packet toward the NIC and utilize all the accelerators that reside on the BlueField DPU (e.g., encryption/decryption, hash computation, compression/decompression).

The DPA platform has efficient DMA accelerators that enable the different execution units to access any memory location accessible by the NIC in parallel and without contention. This includes both synchronous and asynchronous DMA operations triggered by the execution units. In addition, the NIC can DMA data to the DPA caches to enable low-latency access and fast processing. For example, a packet received from the wire may be "DMA-gathered" directly to the DPA's last level caches.

© Copyright 2024, NVIDIA. Last updated on May 7, 2024.