User Guide

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CPI Rate (Intel Atom® processor)

Metric Description

Cycles per Instructions Retired is a fundamental performance metric indicating an average amount of time each instruction took to execute, in units of cycles. For Intel Atom processors, the theoretical best CPI per thread is 0.50, but CPI's over 2.0 warrant investigation. High CPI values may indicate latency in the system that could be reduced such as long-latency memory, floating-point operations, non-retired instructions due to branch mispredictions, or instruction starvation in the front-end. Beware that some optimizations such as SIMD will use less instructions per cycle (increasing CPI), and debug code can use redundant instructions creating more instructions per cycle (decreasing CPI).

Possible Issues

The CPI may be too high. This could be caused by issues such as memory stalls, instruction starvation, branch misprediction or long latency instructions. Explore the other hardware-related metrics to identify what is causing high CPI.

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804