5.5.1. Clustering Results

The distance metrics are extracted based on the analysis of the SPEC benchmark workloads. The temporal distance metric is extracted for *PGTH* = 100. The dendrogram in Figure 14 illustrates the results of the AHC method. As shown in this figure, most of the rarely used instructions in Figure 9 are either grouped together or grouped with other closely similar structures. The original ALU can be partitioned into *n* smaller ALUs according to the dendrogram. One can determine the best *n* value, based on *inconsistency coefficients* [122]. However, as the overhead of hardware implementation increases with the number of clusters, we only have to limit *n* to have at most four clusters (ALUs). Here, we present results for partitioning the ALU into three and four smaller ALUs as the energy improvement for two ALUs vanishes away as the power-gating threshold (*PGTH*) increases.

**Figure 14.** Dendrogram illustration of the proposed AHC method for some of the instructions. The instructions are merged bottom-up to form larger clusters.
