Thursday, September 10, 2009

Performance analysis and benchmarking

Main article: Computer performance
Because there are too many programs to test a CPU's speed on all of them, benchmarks were developed. The most famous benchmarks are the SPECint and SPECfp benchmarks developed by Standard Performance Evaluation Corporation and the ConsumerMark benchmark developed by the Embedded Microprocessor Benchmark Consortium EEMBC.
Some important measurements include:
Instructions per second - Most consumers pick a computer architecture (normally Intel IA32 architecture) to be able to run a large base of pre-existing pre-compiled software. Being relatively uninformed on computer benchmarks, some of them pick a particular CPU based on operating frequency (see Megahertz Myth).
FLOPS - The number of floating point operations per second is often important in selecting computers for scientific computations.
Performance per watt - System designers building parallel computers, such as Google, pick CPUs based on their speed per watt of power, because the cost of powering the CPU outweighs the cost of the CPU itself. [1][2]
Some system designers building parallel computers pick CPUs based on the speed per dollar.
System designers building real-time computing systems want to guarantee worst-case response. That is easier to do when the CPU has low interrupt latency and when it has deterministic response. (DSP)
Computer programmers who program directly in assembly language want a CPU to support a full featured instruction set.
Low power - For systems with limited power sources (e.g. solar, batteries, human power).
Small size or low weight - for portable embedded systems, systems for spacecraft.
Environmental impact - Minimizing environmental impact of computers during manufacturing and recycling as well during use. Reducing waste, reducing hazardous materials. (see Green computing).
Some of these measures conflict. In particular, many design techniques that make a CPU run faster make the "performance per watt", "performance per dollar", and "deterministic response" much worse, and vice versa.

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