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ideal CPI

The cycles per instruction a pipeline would reach if nothing ever stalled: 1 for a simple pipeline that starts one instruction per cycle.

Ideal CPI is the CPI with no stall or flush cycles; real CPI = ideal CPI + average stall cycles per instruction, summed over structural, data and control hazards (and, from Chapter 27, memory waits).

Examples

  • A five-stage pipeline with no stalls has an ideal CPI of 1.

See also

control hazard pipeline stall pipeline hazard cycles per instruction
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