A microprocessor chip has instruction pipeline circuitry, and instruction
classification circuitry that classifies instructions as they are
executed into a small number of classes and records a classification code
value. An on-chip table has entries corresponding to a range of addresses
of a memory and designed to hold a statistical assessment of a value of
consulting an off-chip table in a memory of the computer. Lookup
circuitry is designed to fetch an entry from the on-chip table as part of
the basic instruction processing cycle of the microprocessor. A mask has
a value set at least in part by a timer. The instruction pipeline
circuitry is controlled based on the value of the on-chip table entry
corresponding to the address of instructions processed, the current value
of the mask, the recorded classification code, and the off-chip table.
