CPU - Performance


The performance or speed of a processor depends on e.g.:

  • and the instructions per clock (IPC),

which together are the factors for the instructions per second (IPS) that the CPU can perform.

CPU performance = throughput ?

Comparisons between different types of processors are difficult because performance varies depending on the type of task. See CPU - Benchmark

Se also: CPU - (Metrics|Counter)

Clock Speed

Clock speed is the biggest contributor to power. Chip manufactures (Intel, esp.) pushed clock speeds very hard in the 90s and early 2000s. Doubling the clock speed increases power by 2-8x. Clock speed scaling is essentially finished. What’s Next: Parallelism. This is all the rage right now (multi-processor).

The performance of the memory hierarchy also greatly affects processor performance, an issue barely considered in Million IPS (MIPS) calculations.

The most “regular” computations, fast CPUs still seem to idle for too many cycles while they wait for memory to catch up.

Other factors

While clock rates (See cpu time) are a valid way of comparing the performance of different speeds of the same model and type of processor, other factors such as:

can greatly affect the performance when considering different processors.

For example, one processor may take one clock cycle to add two numbers and another clock cycle to multiply by a third number, whereas another processor may do the same calculation in one clock cycle.

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