Daniel Lipetz

Self Checking in Current Floating-Point Units

High performance microprocessors are protected against transient and early end of life failures using a variety of error detection and fault isolation technologies. Execution units can be protected with duplication, parity prediction, or residue checking. Residue checking has an advantage due to its small size. A modulus is selected based on the radix of the numbers being checked. In a decimal floating-point unit there are two types of numbers in different bases. There are base 10 decimal numbers and base 2 integers being used. A residue checking system that makes it easy to check both base 2 and 10 numbers is discussed. Current state of the art designs that are currently in use are described as well as a novel hybrid moduli 9 and 3 residue system. The checking systems for the decimal and binary floating-point units of some recent IBM microprocessors including the Power6, Power7, z10, and z196 microprocessors are detailed.

Two level bulk preload branch prediction

This paper describes the large capacity hierarchical branch predictor in the 5.5 GHz IBM zEnterprise EC12 microprocessor. Performance analyses in a simulation model and on zEC12 hardware demonstrate the benefit of this hierarchy compared to a smaller one level predictor. Novel structures and algorithms for two level branch prediction are presented. Prediction information about multiple branches is bulk transferred from the second level into the first upon detecting a perceived miss in the first level. The second level does not directly make branch predictions. Access to the second level is limited when it is unlikely to be productive. The second level is systematically searched in an order that is likely to provide hits as early as possible. On the workloads analyzed in the simulation model, measurements show a maximum core performance benefit of 13.8%. On the two workloads analyzed on zEC12 hardware 3.4% and 5.3% system performance improvements are achieved.