Register Renaming via Dual-Channel Segmentation
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Solution Overview
Problem
Register renaming techniques in data processing systems face challenges with high gate count, power consumption, and pipeline bottlenecks when handling a large number of register mappings, particularly in small, inexpensive, and power-efficient processors, where stalling instructions can lead to further inefficiencies.
Innovation Solution
Implementing a dual-channel approach within the register renaming circuitry, where an initial set of register mappings is performed on a main channel for immediate processing, and the remaining mappings are done on a background channel concurrently with other instructions, utilizing a buffer memory to manage the ordering and ensure consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If register renaming is performed for a large number of registers in parallel, then all register mappings are completed simultaneously, but the gate count and power consumption increase disadvantageously
Solution Approach 1:
The patent divides the register renaming operation into two distinct segments: a first number of register mappings handled in parallel through conventional circuitry, and a second number of register mappings processed sequentially in the background. This segmentation allows the system to maintain high throughput for the initial batch while avoiding the need for excessively complex parallel circuitry that would be required to handle all mappings simultaneously, thus resolving the contradiction between productivity and device complexity.
2Productivity
If register renaming is performed for a large number of registers in parallel, then all register mappings are completed simultaneously, but the power consumption increases disadvantageously
Solution Approach 1:
The patent segments the power-consuming register renaming operations into an initial parallel phase and a subsequent sequential background phase. By limiting the parallel phase to a manageable first number of mappings, the instantaneous power consumption is controlled. The remaining mappings are processed sequentially in the background, spreading their power consumption over time rather than concentrating it all at once, thus resolving the contradiction between productivity and power consumption.
3Productivity
If the instruction pipeline is widened to pass more renamed register specifiers in parallel, then register renaming capacity increases, but the area penalty and power consumption increase disadvantageously
Solution Approach 1:
The patent segments the register specifier passing operation into an initial batch transmitted through the conventional instruction pipeline, and remaining specifiers transmitted later through the same pipeline via background operations. This eliminates the need to widen the pipeline to accommodate all specifiers simultaneously, maintaining a narrow, area-efficient pipeline while still achieving high overall throughput through the combination of initial parallel processing and subsequent background processing.
4Reliability
If instructions are stalled to allow register renaming to be completed, then renaming accuracy is maintained, but following program instructions are disadvantageously stalled
Solution Approach 1:
The patent performs preliminary register renaming for an initial set of registers before the instruction is fully dispatched, allowing the instruction to proceed without stalling. The renaming is initiated in advance for as many registers as can be handled by the available circuitry, ensuring that critical register mappings are ready before execution begins, while remaining mappings are completed in the background without blocking the instruction flow, thus resolving the contradiction between reliability and productivity.
Data Source
AI summary
A processor 2 utilising register renaming executes program instructions requiring a large number of architectural register specifiers to be renamed by dividing the renaming tasks into an initial set and a remaining set. The initial set are performed first and the results passed via a main channel 32 for further processing. The remaining set are performed in sequence with the results being passed via a background channel 34 for further processing. This technique is particularly useful for performing renaming operations for load/store multiple LDM instructions.