## Computation Efficiency

An important sub-metric within the *Global Efficiency* ratio is the
*Computation Efficiency* (CompE), which are the ratios of total time in useful
computation summed over all processes.

For strong scaling (i.e., problem size is constant) it is the ratio of total
time in useful computation for a reference case (e.g., on 1 process or 1
compute node) to the total time as the number of processes (or nodes) is
increased. For CompE to have a value of 1000‰ this time must remain
constant regardless of the number of processes.

Insight into possible causes of poor computation scaling can be investigated
using metrics devised from processor hardware counter data. Two causes of poor
computational scaling are:

- Dividing work over additional processes increases the total computation
required.
- Using additional processes leads to contention for shared resources.

We investigate these two causes by analysing the *Instruction Efficiency* (IE),
the *Instructions Per Cycle* (IPCE) Efficiency, and the *Frequency Efficiency*
(FE).

Programs reporting issues with Computation Efficiency:
FFTXlib ·