Operand Cache Register Renaming for Power and Latency Reduction
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Solution Overview
Problem
Modern high-performance CPU designs face power and latency issues due to large register files, which increase the distance data must travel and contribute to higher power consumption and longer latency during instruction execution, especially as more execution units are added.
Innovation Solution
Implementing an operand cache within the execution unit of a CPU that stores frequently used operands, allowing instructions to read from either the physical register file or the operand cache based on power consumption analysis, thereby reducing register file reads and minimizing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a large physical register file is used to store all operands, then all operands can be stored centrally, but power consumption increases and latency increases due to longer data travel distance
Solution Approach 1:
The patent divides the large physical register file into multiple smaller register files distributed across different locations in the CPU architecture. Each execution unit has its own local register file, reducing the distance data must travel and lowering power consumption while still maintaining the ability to store all necessary operands.
Solution Approach 2:
The patent introduces a register renaming unit as an intermediary between the physical register files and execution units. This unit manages the mapping between architectural registers and physical register files, enabling efficient operand access without requiring execution units to directly access distant register files, thus reducing latency and power consumption.
2Quantity of substance
If a large physical register file is used to store all operands, then all operands can be stored centrally, but the distance data must travel increases leading to longer latency
Solution Approach 1:
The patent segments the register file into multiple smaller files distributed closer to execution units. This reduces the physical distance data must travel, thereby reducing latency while still maintaining comprehensive operand storage capability through the distributed architecture.
Solution Approach 2:
The patent implements operand buffering in the register renaming unit, which pre-loads frequently accessed operands into local registers or caches before they are needed by execution units. This preliminary action reduces the latency when execution units need to access these operands.
3Productivity
If more execution units are added to increase processing capability, then productivity increases, but the total die area required increases and register file reads become more power-intensive
Solution Approach 1:
The patent assigns separate local register files to each execution unit, allowing each unit to have its own small operand storage. This segmented approach increases processing capability by supporting more execution units while keeping the die area manageable, as each unit only needs a small local register file rather than all units sharing a large centralized register file.
Solution Approach 2:
The patent implements local register files at each execution unit, providing locally optimized storage close to the computation logic. This local quality approach reduces the need for long-distance data transfers and lowers power consumption per execution unit, enabling higher overall productivity without proportionally increasing total die area.
4Extent of automation
If register renaming is implemented using a large physical register set, then out-of-order execution is enabled, but power consumption increases due to frequent register file reads
Solution Approach 1:
The patent segments the physical register set into multiple smaller register files distributed across different locations. Each execution unit has access to its own local register file, reducing the distance and power required for register reads during out-of-order execution while maintaining the renaming capability for performance optimization.
Solution Approach 2:
The register renaming unit serves as an intermediary that manages the mapping between architectural and physical registers, and also acts as a buffer that can supply operands to execution units without requiring frequent reads from distant register files, thereby reducing power consumption during out-of-order execution.
Data Source
AI summary
A system and a method are disclosed to process instructions in an execution unit (EU) that includes an operand cache (OC). The OC stores a copy of at least one frequently used operand stored in a physical register file (PRF). The EU may process instructions using operands obtained from the PRF or from the OC. In the first mode, an OC renaming unit (OC-REN) indicates to the EU to process instructions using operands obtained from the OC if processing the instructions using operands obtained from the OC uses less power than using operands obtained from the PRF. In the second mode, the OC-REN indicates to the EU to process the instructions using operands obtained from the PRF if processing the instructions using operands obtained from the PRF uses less power than using operands obtained from the OC.