A processor (102; 600; 700; 870, 880) comprising: a plurality of cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) grouped into a plurality of clusters (202, 214, 218, 222), wherein the clusters (202, 214, 218, 222) are formed based on a corresponding operating voltage of each core (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) at each of a plurality of frequencies, such that the cores in each cluster have a similar voltage-frequency, V-F, characteristics, wherein each cluster (202, 214, 218, 222) comprises a unique set of cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) and at least one cluster (202, 214, 218, 222) includes at least two of the cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a); further comprising a power control unit, PCU (110; 655; 756; 840, 850; 913, 915), comprising frequency/voltage control logic (116; 757; 842, 852), responsive to a frequency change request from a first core (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) of a first cluster of cores (202, 214, 218, 222), to determine an operating voltage for the first core (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) from a first cluster V-F table associated with the first cluster (202, 214, 218, 222), wherein the V-F table for each cluster uniquely specifies a corresponding operating voltage at each of a plurality of frequencies of operation of the cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) of the respective cluster (202, 214, 218, 222), and wherein the V-F table for each cluster is constructed based on maximum voltages at predetermined frequencies of the V-F characteristics of the cores within the respective cluster. a plurality of cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) grouped into a plurality of clusters (202, 214, 218, 222), wherein the clusters (202, 214, 218, 222) are formed based on a corresponding operating voltage of each core (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) at each of a plurality of frequencies, such that the cores in each cluster have a similar voltage-frequency, V-F, characteristics, wherein each cluster (202, 214, 218, 222) comprises a unique set of cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) and at least one cluster (202, 214, 218, 222) includes at least two of the cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a); further comprising a power control unit, PCU (110; 655; 756; 840, 850; 913, 915), comprising frequency/voltage control logic (116; 757; 842, 852), responsive to a frequency change request from a first core (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) of a first cluster of cores (202, 214, 218, 222), to determine an operating voltage for the first core (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) from a first cluster V-F table associated with the first cluster (202, 214, 218, 222), wherein the V-F table for each cluster uniquely specifies a corresponding operating voltage at each of a plurality of frequencies of operation of the cores (104 0 -104 N; 610 a -610 n; 710 0 -710 n; 874a, 884a) of the respective cluster (202, 214, 218, 222), and wherein the V-F table for each cluster is constructed based on maximum voltages at predetermined frequencies of the V-F characteristics of the cores within the respective cluster.