Dataflow architecture is a

dataflow In computing, dataflow is a broad concept, which has various meanings depending on the application and context. In the context of software architecture, data flow relates to stream processing or reactive programming. Software architecture Da ...

-based

computer architecture In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, the ...

that directly contrasts the traditional

von Neumann architecture The von Neumann architecture — also known as the von Neumann model or Princeton architecture — is a computer architecture based on a 1945 description by John von Neumann, and by others, in the '' First Draft of a Report on the EDVAC''. T ...

control flow In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an '' ...

architecture. Dataflow architectures have no

program counter The program counter (PC), commonly called the instruction pointer (IP) in Intel x86 and Itanium microprocessors, and sometimes called the instruction address register (IAR), the instruction counter, or just part of the instruction sequencer, i ...

, in concept: the executability and execution of instructions is solely determined based on the availability of input arguments to the instructions, so that the order of instruction execution is unpredictable, i.e., behavior is nondeterministic. Although no commercially successful general-purpose computer hardware has used a dataflow architecture, it has been successfully implemented in specialized hardware such as in

digital signal processing Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are ...

, network routing,

graphics processing Computer graphics is a sub-field of computer science which studies methods for digitally synthesizing and manipulating visual content. Although the term often refers to the study of three-dimensional computer graphics, it also encompasses two-di ...

telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', "remote", an ...

, and more recently in data warehousing, and

artificial intelligence Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech ...

(as: polymorphic dataflow Convolution Engine, structure-driven, dataflow scheduling). It is also very relevant in many software architectures today including

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

engine designs and

parallel computing Parallel computing is a type of computation in which many calculations or processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different f ...

frameworks. Synchronous dataflow architectures tune to match the workload presented by real-time data path applications such as wire speed packet forwarding. Dataflow architectures that are deterministic in nature enable programmers to manage complex tasks such as processor load balancing, synchronization and accesses to common resources. Meanwhile, there is a clash of terminology, since the term ''

'' is used for a subarea of parallel programming: for

dataflow programming In computer programming, dataflow programming is a programming paradigm that models a program as a directed graph of the data flowing between operations, thus implementing dataflow principles and architecture. Dataflow programming languages share ...

History

Hardware architectures for dataflow was a major topic in

research in the 1970s and early 1980s.

Jack Dennis Jack Bonnell Dennis (born October 13, 1931) is a computer scientist and Emeritus Professor of Computer Science and Engineering at Massachusetts Institute of Technology. The work of Dennis in computer systems and computer languages is recogniz ...

of MIT pioneered the field of static dataflow architectures while the Manchester Dataflow MachineManchester Dataflow Research Project, Research Reports: Abstracts, September 1997
/ref> and MIT Tagged Token architecture were major projects in dynamic dataflow. The research, however, never overcame the problems related to: * Efficiently broadcasting data tokens in a massively parallel system. * Efficiently dispatching instruction tokens in a massively parallel system. * Building

content-addressable memory Content-addressable memory (CAM) is a special type of computer memory used in certain very-high-speed searching applications. It is also known as associative memory or associative storage and compares input search data against a table of stored d ...

(CAM) large enough to hold all of the dependencies of a real program. Instructions and their data dependencies proved to be too fine-grained to be effectively distributed in a large network. That is, the time for the instructions and tagged results to travel through a large connection network was longer than the time to do many computations. Nonetheless,

out-of-order execution In computer engineering, out-of-order execution (or more formally dynamic execution) is a paradigm used in most high-performance central processing units to make use of instruction cycles that would otherwise be wasted. In this paradigm, a proces ...

(OOE) has become the dominant computing paradigm since the 1990s. It is a form of restricted dataflow. This paradigm introduced the idea of an ''execution window''. The ''execution window'' follows the sequential order of the von Neumann architecture, however within the window, instructions are allowed to be completed in data dependency order. This is accomplished in CPUs that dynamically tag the data dependencies of the code in the execution window. The logical complexity of dynamically keeping track of the data dependencies, restricts ''OOE''

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...

s to a small number of execution units (2-6) and limits the execution window sizes to the range of 32 to 200 instructions, much smaller than envisioned for full dataflow machines.

Dataflow architecture topics

Static and dynamic dataflow machines

Designs that use conventional memory addresses as data dependency tags are called static dataflow machines. These machines did not allow multiple instances of the same routines to be executed simultaneously because the simple tags could not differentiate between them. Designs that use

(CAM) are called dynamic dataflow machines. They use tags in memory to facilitate parallelism.

Compiler

Normally, in the control flow architecture,

compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...

s analyze program

source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the ...

for data dependencies between instructions in order to better organize the instruction sequences in the binary output files. The instructions are organized sequentially but the dependency information itself is not recorded in the binaries. Binaries compiled for a dataflow machine contain this dependency information. A dataflow compiler records these dependencies by creating unique tags for each dependency instead of using variable names. By giving each dependency a unique tag, it allows the non-dependent code segments in the binary to be executed ''out of order'' and in parallel. Compiler detects the loops, break statements and various programming control syntax for data flow.

Programs

Programs are loaded into the CAM of a dynamic dataflow computer. When all of the tagged operands of an instruction become available (that is, output from previous instructions and/or user input), the instruction is marked as ready for execution by an

execution unit In computer engineering, an execution unit (E-unit or EU) is a part of the central processing unit (CPU) that performs the operations and calculations as instructed by the computer program. It may have its own internal control sequence unit (not ...

. This is known as ''activating'' or ''firing'' the instruction. Once an instruction is completed by an execution unit, its output data is sent (with its tag) to the CAM. Any instructions that are dependent upon this particular datum (identified by its tag value) are then marked as ready for execution. In this way, subsequent instructions are executed in proper order, avoiding

race condition A race condition or race hazard is the condition of an electronics, software, or other system where the system's substantive behavior is Sequential logic, dependent on the sequence or timing of other uncontrollable events. It becomes a software ...

s. This order may differ from the sequential order envisioned by the human programmer, the programmed order.

Instructions

An instruction, along with its required data operands, is transmitted to an execution unit as a packet, also called an ''instruction token''. Similarly, output data is transmitted back to the CAM as a ''data token''. The packetization of instructions and results allows for parallel execution of ready instructions on a large scale. Dataflow networks deliver the instruction tokens to the execution units and return the data tokens to the CAM. In contrast to the conventional

, data tokens are not permanently stored in memory, rather they are transient messages that only exist when in transit to the instruction storage.

References

{{Hardware acceleration Hardware acceleration Classes of computers Computer architecture