Register Windows for Parallel Loop Iterations
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Solution Overview
Problem
In highly parallel strand-based architectures, the dynamic register renaming technique used in superscalar architectures is inefficient due to out-of-order instruction fetch and execution, limiting the ability to exploit inter-iteration parallelism in loops effectively.
Innovation Solution
An efficient register allocation scheme is implemented, where a binary translator decomposes loops into strands and allocates separate iteration windows for each loop iteration, allowing strands to execute with different register sets, thereby avoiding register overwriting and enabling high levels of instruction-level parallelism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dynamic register renaming technique is used in superscalar architectures, then inter-iteration parallelism can be exploited through out-of-order execution, but the technique becomes inefficient in highly parallel strand-based architectures due to out-of-order instruction fetch and the need to support much larger execution width
Solution Approach 1:
The patent divides the loop iterations into multiple segments or windows, where each window contains a subset of iterations that can be executed in parallel. This segmentation allows the system to manage register allocation in discrete blocks rather than requiring complex dynamic renaming across all iterations, thereby reducing hardware complexity while maintaining high parallelism.
Solution Approach 2:
The patent introduces a new dimension for register allocation by using iteration windows that add a temporal and spatial structure to register management. Instead of relying solely on complex renaming logic, the system organizes registers into windows corresponding to different iteration segments, enabling parallel execution across multiple dimensions of iteration space.
2Productivity
If multiple loop iterations are processed simultaneously via multiple strands, then out-of-order fetch and execution is enabled, but dynamic register renaming becomes inapplicable due to the need to support much larger execution width than practical renaming hardware can afford
Solution Approach 1:
The patent segments the large execution width requirement into multiple smaller iteration windows, each handling a manageable subset of iterations. This segmentation allows practical renaming hardware to handle each window independently while the system as a whole achieves support for much larger execution width through parallel window processing.
Solution Approach 2:
The patent applies partial renaming within each iteration window rather than attempting to rename all registers across all iterations simultaneously. This partial action approach allows the system to achieve the effect of supporting large execution width by processing iterations in batches, using practical renaming hardware for each batch without requiring impractical full-system renaming capacity.
Data Source
AI summary
An apparatus includes a register file and a binary translator to create a plurality of strands and a plurality of iteration windows, where each iteration window of the plurality of iteration windows is allocated a set of continuous registers of the register file. The apparatus further includes a buffer to store strand documentation for a strand from the plurality of strands, where the strand documentation for the strand is to include an indication of a current register base for the strand. The apparatus further includes an execution circuit to execute an instruction to update the current register base for the strand in the strand documentation for the strand based on a fixed step value and an iteration window size.