Computation Efficiency is a ratio 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 Computation Efficiency to have a value of 1 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

and we investigate these using Instruction Efficiency and IPC Efficiency.