GPU Coalescing Operand Register File for Fewer Reads
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Solution Overview
Problem
The high power consumption and performance limitations of register files in GPUs are due to frequent access and limited ports, leading to port contention and inefficient register operations.
Innovation Solution
A compiler-assisted coalescing operand register file (CORF) combines reads to multiple registers required by a single instruction into a single physical read, utilizing register packing and compiler hints to identify commonly accessed register pairs, and re-architecting the register file organization to enable coalescing across different physical registers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the register file size is increased to support more concurrent thread contexts, then the ability to maintain thread states and support fast context switching is improved, but the dynamic power consumption and area occupied by the register file increases
Solution Approach 1:
The patent combines multiple narrow-width register files into a single unified register file structure. This merging allows the system to maintain support for multiple concurrent thread contexts while reducing the total number of separate register file instances, thereby reducing overall dynamic power consumption and area utilization.
Solution Approach 2:
The unified register file is designed to serve multiple functions: it maintains thread states for numerous concurrent contexts, supports fast context switching, and reduces power consumption compared to having separate register files for each context. This multi-functional design allows a single structure to replace what would traditionally require multiple specialized register files.
2Productivity
If the number of ports on the operand collectors and register file banks is increased to reduce serialization, then the performance and throughput of register operations is improved, but the device complexity and area increase
Solution Approach 1:
The register file is divided into multiple banks, each with its own ports. This segmentation allows parallel access to different portions of the register file, reducing serialization and improving throughput without requiring a single complex high-port-count structure. The segmented approach distributes the complexity across multiple simpler units.
Solution Approach 2:
The patent introduces a bank dimension to the register file architecture, organizing registers into multiple banks that can be accessed in parallel. This dimensional organization allows the system to achieve high throughput by exploiting parallelism across banks rather than requiring excessive ports on a single monolithic structure, thereby managing complexity more effectively.
3Quantity of substance
If register packing is used to co-locate narrow-width operands in the same physical register, then the number of physical register entries is reduced, but the complexity of register allocation and management increases
Solution Approach 1:
The system changes the width parameter of physical registers by introducing variable-width register entries that can accommodate narrow-width operands. Instead of using fixed full-width registers, the register file supports registers of different widths, allowing multiple narrow operands to be packed into a single physical register entry, thereby reducing the total number of physical registers required.
Solution Approach 2:
The patent introduces an intermediary layer between the architectural register file and the physical register implementation. This intermediary handles the complexity of register packing, allocation, and management, shielding the rest of the system from these complexities while enabling efficient use of physical register entries through packing of narrow-width operands.
4Speed
If the register file is accessed frequently to maintain thread states, then the responsiveness and performance of context switching is improved, but the dynamic power consumption increases
Solution Approach 1:
By merging multiple register files into a unified structure, the system reduces the total number of access operations required for context switching. Instead of accessing multiple separate register files, the unified structure allows more efficient access patterns that maintain fast context switching performance while reducing the cumulative power consumption of frequent accesses.
Data Source
AI summary
A system and method for register coalescing is described. The system comprises a CORF, a coalescing-aware register file design for GPUs that simultaneously reduces the leakage and dynamic access power, while improving the overall performance of the GPU. CORF achieves these properties by enabling the reads to multiple operands that are packed together to be coalesced, reducing the number of reads to the RF, and improving dynamic energy and performance. CORF combines compiler-assisted register allocation with a reorganized register file (CORF++) in order to maximize operand coalescing opportunities.