Kilo-instruction Processors

Due to the difference between processor speed and memory speed, the latter has steadily appeared further away in cycles to the processor. Superscalar out-of-order processors cope with these increasing latencies by having more in-flight instructions from where to extract ILP. With coming latencies of 500 cycles and more, this will eventually derive in what we have called Kilo-Instruction Processors, which will have to handle thousands of in-flight instructions. Managing such a big number of in-flight instructions must imply a microarchitectural change in the way the re-order buffer, the instructions queues and the physical registers are handled, since simply up-sizing these resources is technologically unfeasible. In this paper we present a survey of several techniques which try to solve these problems caused by thousands of in-flight instructions.