Purpose[ edit ] As computer architecture advanced, it became more difficult to compare the performance of various computer systems simply by looking at their specifications. Therefore, tests were developed that allowed comparison of different architectures. For example, Pentium 4 processors generally operated at a higher clock frequency than Athlon XP or PowerPC processors, which did not necessarily translate to more computational power; a processor with a slower clock frequency might perform as well as or even better than a processor operating at a higher frequency. See BogoMips and the megahertz myth. Benchmarks are designed to mimic a particular type of workload on a component or system.
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Purpose[ edit ] As computer architecture advanced, it became more difficult to compare the performance of various computer systems simply by looking at their specifications. Therefore, tests were developed that allowed comparison of different architectures. For example, Pentium 4 processors generally operated at a higher clock frequency than Athlon XP or PowerPC processors, which did not necessarily translate to more computational power; a processor with a slower clock frequency might perform as well as or even better than a processor operating at a higher frequency.
See BogoMips and the megahertz myth. Benchmarks are designed to mimic a particular type of workload on a component or system. Synthetic benchmarks do this by specially created programs that impose the workload on the component. Application benchmarks run real-world programs on the system. While application benchmarks usually give a much better measure of real-world performance on a given system, synthetic benchmarks are useful for testing individual components, like a hard disk or networking device.
Benchmarks are particularly important in CPU design , giving processor architects the ability to measure and make tradeoffs in microarchitectural decisions. For example, if a benchmark extracts the key algorithms of an application, it will contain the performance-sensitive aspects of that application. Running this much smaller snippet on a cycle-accurate simulator can give clues on how to improve performance.
Computer manufacturers are known to configure their systems to give unrealistically high performance on benchmark tests that are not replicated in real usage. For instance, during the s some compilers could detect a specific mathematical operation used in a well-known floating-point benchmark and replace the operation with a faster mathematically equivalent operation. However, such a transformation was rarely useful outside the benchmark until the mids, when RISC and VLIW architectures emphasized the importance of compiler technology as it related to performance.
Benchmarks are now regularly used by compiler companies to improve not only their own benchmark scores, but real application performance. Nevertheless, CPUs with many execution units often complete real-world and benchmark tasks in less time than the supposedly faster high-clock-rate CPU. Given the large number of benchmarks available, a manufacturer can usually find at least one benchmark that shows its system will outperform another system; the other systems can be shown to excel with a different benchmark.
Manufacturers commonly report only those benchmarks or aspects of benchmarks that show their products in the best light. They also have been known to mis-represent the significance of benchmarks, again to show their products in the best possible light. Taken together, these practices are called bench-marketing. Ideally benchmarks should only substitute for real applications if the application is unavailable, or too difficult or costly to port to a specific processor or computer system. Challenges[ edit ] Benchmarking is not easy and often involves several iterative rounds in order to arrive at predictable, useful conclusions.
Interpretation of benchmarking data is also extraordinarily difficult. Here is a partial list of common challenges: Vendors tend to tune their products specifically for industry-standard benchmarks.
Norton SysInfo SI is particularly easy to tune for, since it mainly biased toward the speed of multiple operations. Use extreme caution in interpreting such results. Some vendors have been accused of "cheating" at benchmarks — doing things that give much higher benchmark numbers, but make things worse on the actual likely workload. Examples of unmeasured qualities of service include security, availability, reliability, execution integrity, serviceability, scalability especially the ability to quickly and nondisruptively add or reallocate capacity , etc.
There are often real trade-offs between and among these qualities of service, and all are important in business computing. Transaction Processing Performance Council Benchmark specifications partially address these concerns by specifying ACID property tests, database scalability rules, and service level requirements.
In general, benchmarks do not measure Total cost of ownership. However, the costs are necessarily only partial, and vendors have been known to price specifically and only for the benchmark, designing a highly specific "benchmark special" configuration with an artificially low price. Even a tiny deviation from the benchmark package results in a much higher price in real world experience.
Facilities burden space, power, and cooling. When more power is used, a portable system will have a shorter battery life and require recharging more often. There are real trade-offs as most semiconductors require more power to switch faster. See also performance per watt. In some embedded systems, where memory is a significant cost, better code density can significantly reduce costs.
Vendor benchmarks tend to ignore requirements for development, test, and disaster recovery computing capacity. Vendors only like to report what might be narrowly required for production capacity in order to make their initial acquisition price seem as low as possible. Benchmarks are having trouble adapting to widely distributed servers, particularly those with extra sensitivity to network topologies. The emergence of grid computing , in particular, complicates benchmarking since some workloads are "grid friendly", while others are not.
Users can have very different perceptions of performance than benchmarks may suggest. In particular, users appreciate predictability — servers that always meet or exceed service level agreements.
Benchmarks tend to emphasize mean scores IT perspective , rather than maximum worst-case response times real-time computing perspective , or low standard deviations user perspective. Many benchmarks focus on one application, or even one application tier, to the exclusion of other applications.
Most data centers are now implementing virtualization extensively for a variety of reasons, and benchmarking is still catching up to that reality where multiple applications and application tiers are concurrently running on consolidated servers. There are few if any high quality benchmarks that help measure the performance of batch computing, especially high volume concurrent batch and online computing.
Batch computing tends to be much more focused on the predictability of completing long-running tasks correctly before deadlines, such as end of month or end of fiscal year. Many important core business processes are batch-oriented and probably always will be, such as billing. Benchmarking institutions often disregard or do not follow basic scientific method. This includes, but is not limited to: small sample size, lack of variable control, and the limited repeatability of results.
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