IPC
Metric Description
Instructions Retired per Cycle, or IPC shows
average number of retired instructions per cycle. Modern superscalar processors
issue up to four instructions per cycle, suggesting a theoretical best IPC of
4. But various effects (long-latency memory, floating-point, or SIMD
operations; non-retired instructions due to branch mispredictions; instruction
starvation in the front-end) tend to pull the observed IPC down. A IPC of 1 is
generally considered acceptable for HPC applications but different application
domains will have very different expected values. Nonetheless, IPC is an
excellent metric for judging an overall potential for application performance
tuning.
Possible Issues
The IPC may be too low. 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 low IPC.