1. Introduction to Bifrost

1.1. Bifrost is …

A stream processing framework, created to ease the development of high-throughput processing CPU/GPU pipelines. It is specifically designed for digital signal processing (DSP) applications within radio astronomy. A portable C API is provided, along with C++ and Python wrappers.

The heart of bifrost is a flexible ring buffer implementation that allows different signal processing blocks to be connected to form a pipeline. Each block may be assigned to a CPU core, and the ring buffers are used to transport data to and from blocks. Processing blocks may be run on either the CPU or GPU, and the ring buffer will take care of memory copies between the CPU and GPU spaces.

1.2. Core concepts

1.2.1. Streaming data

The purpose of bifrost is to allow rapid development of streaming DSP pipelines; that is, it is designed for stream-like data. A simple example of a data stream is the time series voltage data from a radio telescope’s digitizer card. Unlike file-like data, stream-like data has no well defined start and stop points. One can of course take a series of files, each containing a chunk of a time stream, and treat them as a stream.

1.2.2. Pipelines

A pipeline is a programming implementation where data processing elements are daisy-chained together and stream data are pushed through them – like water through a pipe. The data processing elements all run at once, each processing different bits of data which “flow” through the pipeline.

Pipelining can significantly improve a code’s performance (image a road system with only one car on it at one time: that would be an ‘unpipelined’ transport system!). Nevertheless, if there is a particularly slow processing element, the flow of the pipeline will be limited by that element’s output data rate– this is known as a bottleneck.

1.2.3. Ring buffers

A common way to implement pipelines is to connect data processing elements together with buffer memory storage. Bifrost uses this approach, and the specific implementation is known as a ring buffer, or just ring. The ring is shared between processing elements: one element writes to the ring, while the other processing element reads from the ring.

1.2.4. Blocks

In Bifrost, anything that does something to a data stream is called a block. Conceptually, there are three kinds of blocks: * tasks: A block that reads from a ring, transforms the data in some way, and writes it out to an output ring. * source: A block that generates data, or loads it from outside the pipeline (e.g. a file or an Ethernet stream), and writes it to an output ring. * sink: A block that reads data from an input ring and plots it, or writes it to file, or generally does something without any pipeline output.

A simple pipeline would be a source block (e.g. file read), connected to a task block (compute average), connected to a sink block (plot time series of moving averaged data).

1.3. More

Further explanation of Bifrost’s concepts is detailed in the paper: https://arxiv.org/abs/1708.00720