Dhrystone is a

synthetic Synthetic may refer to: Science * Synthetic biology * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic elements, chemical elements that are not naturally found on Earth and therefore have to be created in ...

computing

benchmark Benchmark may refer to: Business and economics * Benchmarking, evaluating performance within organizations * Benchmark price * Benchmark (crude oil), oil-specific practices Science and technology * Experimental benchmarking, the act of defining a ...

program developed in 1984 by Reinhold P. Weicker intended to be representative of system (

integer An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...

) programming. The Dhrystone grew to become representative of general processor (

CPU A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary processor in a given computer. Its electronic circuitry executes instructions of a computer program, such as arithmetic, log ...

) performance. The name "Dhrystone" is a pun on a different benchmark algorithm called Whetstone, which emphasizes

floating point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a signed sequence of a fixed number of digits in some base) multiplied by an integer power of that base. Numbers of this form ...

performance. With Dhrystone, Weicker gathered meta-data from a broad range of software, including programs written in FORTRAN,

PL/1 PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language initially developed by IBM. It is designed for scientific, engineering, business and system programming. It has b ...

, SAL,

ALGOL 68 ALGOL 68 (short for ''Algorithmic Language 1968'') is an imperative programming language member of the ALGOL family that was conceived as a successor to the ALGOL 60 language, designed with the goal of a much wider scope of application and ...

, and Pascal. He then characterized these programs in terms of various common constructs: procedure calls, pointer

indirection In computer programming, an indirection (also called a reference) is a way of referring to something using a name, reference, or container instead of the value itself. The most common form of indirection is the act of manipulating a value through ...

s, assignments, etc. From this he wrote the Dhrystone benchmark to correspond to a representative mix. Dhrystone was published in Ada, with the C version for

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

developed by Rick Richardson ("version 1.1") greatly contributing to its popularity.

Dhrystone vs. Whetstone

The Dhrystone benchmark contains no

operations, thus the name is a pun on the then-popular Whetstone benchmark for floating point operations. The output from the benchmark is the number of Dhrystones per second (the number of iterations of the main code loop per second). Both Whetstone and Dhrystone are ''synthetic'' benchmarks, meaning that they are simple programs that are carefully designed to statistically mimic the processor usage of some common set of programs. Whetstone, developed in 1972, originally strove to mimic typical Algol 60 programs based on measurements from 1970, but eventually became most popular in its Fortran version, reflecting the highly numerical orientation of computing in the 1960s.

Issues addressed by Dhrystone

Dhrystone's eventual importance as an indicator of general-purpose ("integer") performance of new computers made it a target for commercial compiler writers. Various modern compiler

static code analysis In computer science, static program analysis (also known as static analysis or static simulation) is the analysis of computer programs performed without executing them, in contrast with dynamic program analysis, which is performed on programs duri ...

techniques (such as elimination of dead code: for example, code which uses the processor but produces internal results which are not used or output) make the use and design of synthetic benchmarks more difficult. Version 2.0 of the benchmark, released by Weicker and Richardson in March 1988, had a number of changes intended to foil a range of compiler techniques. Yet it was carefully crafted so as not to change the underlying benchmark. This effort to foil compilers was only partly successful. Dhrystone 2.1, released in May of the same year, had some minor changes and remains the current definition of Dhrystone. Other than issues related to compiler optimization, various other issues have been cited with the Dhrystone. Most of these, including the small code size and small data set size, were understood at the time of its publication in 1984. More subtle is the slight over-representation of string operations, which is largely language-related: both Ada and Pascal have strings as normal variables in the language, whereas C does not, so what was simple variable assignment in reference benchmarks became buffer copy operations in the C library. Another issue is that the score reported does not include information which is critical when comparing systems such as which compiler was used, and what optimizations. Dhrystone remains remarkably resilient as a simple benchmark, but its continuing value in establishing true performance is questionable. It is easy to use, well documented, fully self-contained, well understood, and can be made to work on almost any system. In particular, it has remained in broad use in the embedded computing world, though the recently developed EEMBC benchmark suite, the CoreMark standalone benchmark, HINT, Stream, and even Bytemark are widely quoted and used, as well as more specific benchmarks for the memory subsystem (Cachebench), TCP/IP (TTCP), and many others.

Results

Dhrystone may represent a result more meaningfully than MIPS (million instructions per second) because instruction count comparisons between different instruction sets (e.g.

RISC In electronics and computer science, a reduced instruction set computer (RISC) is a computer architecture designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a comp ...

vs. CISC) can confound simple comparisons. For example, the same high-level task may require many more instructions on a RISC machine, but might execute faster than a single CISC instruction. Thus, the Dhrystone score counts only the number of program iteration completions per second, allowing individual machines to perform this calculation in a machine-specific way. Another common representation of the Dhrystone benchmark is the DMIPS (Dhrystone MIPS) obtained when the Dhrystone score is divided by 1757 (the number of Dhrystones per second obtained on the VAX 11/780, nominally a 1 MIPS machine). Another way to represent results is in DMIPS/MHz, where DMIPS result is further divided by CPU frequency, to allow for easier comparison of CPUs running at different

clock rate Clock rate or clock speed in computing typically refers to the frequency at which the clock generator of a processor can generate pulses used to synchronize the operations of its components. It is used as an indicator of the processor's s ...

Shortcomings

Using Dhrystone as a benchmark has pitfalls: * It features unusual code that is not usually representative of modern real-life programs. * It is susceptible to compiler optimizations. For example, it does a lot of string copying in an attempt to measure string copying performance. However, the strings in Dhrystone are of known constant length and their starts are aligned on natural boundaries, two characteristics usually absent from real programs. Therefore, an optimizer can replace a string copy with a sequence of word moves without any loops, which will be much faster. This optimization consequently overstates system performance, sometimes by more than 30%. * Dhrystone's small code size may fit in the

instruction cache A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, located closer to a processor core, which ...

of a modern CPU, so that

instruction fetch The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions ...

performance is not rigorously tested. Similarly, Dhrystone may also fit completely in the

data cache A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, located closer to a processor core, which ...

, thus not exercising data cache miss performance. To counter fits-in-the-cache problem, the

SPECint SPEC INT is a computer benchmark specification for CPU integer processing power. It is maintained by the Standard Performance Evaluation Corporation (SPEC). SPEC INT is the integer performance testing component of the SPEC test suite. The first ...

benchmark was created in 1988 to include a suite of (initially 8) much larger programs (including a compiler) which could not fit into L1 or L2 caches of that era.

References

External links

* {{cite journal , last=Weicker , first=Reinhold , title=Dhrystone: A Synthetic Systems Programming Benchmark , journal=

Communications of the ACM ''Communications of the ACM'' (''CACM'') is the monthly journal of the Association for Computing Machinery (ACM). History It was established in 1958, with Saul Rosen as its first managing editor. It is sent to all ACM members. Articles are i ...