Register Renaming Cache Replay for Lower RAT Power and Complexity
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Solution Overview
Problem
Register renaming techniques in processors face increasing complexity and power consumption issues due to high allocation widths, leading to power hotspots and timing criticality, especially with the use of register alias tables (RATs), which also incur super-linear increases in dynamic capacitance and timing complexity.
Innovation Solution
Implement a register renaming cache that stores register renaming information for instruction traces between taken branches, allowing for efficient replay of renaming operations through a simple lookup, reducing the reliance on complex RATs and minimizing power consumption and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If register alias tables (RATs) are used for register renaming, then register renaming functionality is achieved, but complexity and power consumption increase super-linearly with allocation width
Solution Approach 1:
The patent divides the register renaming functionality into two separate components: a register rename map for mapping logical registers to physical registers, and a separate inline dependency calculation unit. This segmentation allows each component to be optimized independently, reducing the super-linear complexity growth that occurs when using a monolithic RAT structure.
Solution Approach 2:
The patent extracts the inline dependency calculation from the traditional RAT structure and implements it as a separate unit that operates on the output of the register rename map. This extraction eliminates the need for complex port arrays within the RAT itself, reducing device complexity while maintaining the necessary functionality.
2Adaptability or versatility
If register alias tables (RATs) are used for register renaming, then register renaming functionality is achieved, but power consumption increases and creates power hotspots
Solution Approach 1:
By segmenting the register renaming functionality into a simple rename map and a separate dependency calculation unit, the patent reduces the power consumption of the main RAT structure. The rename map becomes a lightweight lookup table rather than a complex active structure, significantly reducing dynamic power consumption while maintaining functionality.
Solution Approach 2:
The patent replaces the expensive, complex RAT structure with a simpler, cheaper rename map structure that requires less power to operate. The separate dependency calculation unit is only activated when needed, rather than continuously powering complex RAT port arrays, reducing overall power consumption and eliminating power hotspots.
3Adaptability or versatility
If register alias tables (RATs) are used for register renaming, then register renaming operations can be performed, but timing criticality increases affecting core frequency
Solution Approach 1:
The patent segments the register renaming process into two distinct stages: first, a simple lookup in the rename map to determine physical register mappings, and second, a separate dependency calculation step. This segmentation allows the critical path to be shortened, as the rename map lookup is much faster than traditional RAT operations, enabling higher core frequencies.
Solution Approach 2:
By extracting the dependency calculation from the critical path of the RAT operation and implementing it as a separate post-processing step, the patent removes the timing criticality associated with complex RAT port access. This extraction allows the rename map to operate at higher speeds without being constrained by the timing requirements of inline dependency calculations.
4Quantity of substance
If high allocation width is used in RATs, then more registers can be managed, but dynamic capacitance and timing complexity increase super-linearly
Solution Approach 1:
The patent segments the handling of multiple registers into two independent operations: a parallel lookup in the rename map that can handle multiple registers simultaneously, and a sequential dependency calculation that processes the results. This segmentation allows the system to manage high allocation widths without the super-linear timing complexity that would result from trying to handle all register operations in a single monolithic structure.
Solution Approach 2:
The patent extracts the dependency calculation from the register management process and implements it as a separate post-processing step. This extraction allows the rename map to scale to high allocation widths with minimal timing complexity, as the map lookup itself remains simple and fast, while the more complex dependency analysis is performed separately on the already-renamed registers.
Data Source
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AI summary
Techniques for register renaming caching are described. In an embodiment, an apparatus includes a register renaming cache, front-end circuitry, lookup circuitry, and execution circuitry. The register renaming cache is to store register renaming information associated with an instruction trace. The register renaming information is to be learned from a first execution of the instruction trace and is to be used to perform register renaming in connection with a second execution of the instruction trace. The front-end circuitry is to provide, based on the instruction trace, operations for execution. The lookup circuitry to look in the register renaming cache for entries corresponding to the operations. The execution circuitry is to execute the instruction trace.