Dependency Cache for Register Conflict Resolution
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Solution Overview
Problem
Current processors with multiple execution units face challenges in maximizing performance due to dependencies between instructions, which limit parallelism and require complex hardware redesigns, are costly, and are not effective in virtualized or multi-threaded environments where dependencies are hard to predict.
Innovation Solution
A processor with a dependency cache that resolves register access conflicts and optimizes instruction issuance by learning static and dynamic dependencies, allowing instructions to be assigned to execution units based on stored indicators, reducing forwarding latency and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If instructions are issued to parallel execution units without reflecting dependencies, then instruction throughput increases, but execution correctness deteriorates due to register access conflicts
Solution Approach 1:
The control logic performs preliminary analysis of register access conflicts between subsequent instructions before issuing them to execution units. By checking for conflicts in advance and adjusting issuance timing, the system maintains both high throughput and execution correctness without requiring software redesign.
2Productivity
If algorithms and programs are redesigned to fit hardware dependencies, then execution efficiency improves, but development cost and complexity increase
Solution Approach 1:
The processor hardware performs self-service by automatically detecting and resolving register access conflicts through its control logic. This eliminates the need for software to manually optimize for hardware dependencies, allowing programs to run efficiently without special redesign while maintaining correctness.
3Productivity
If more execution units are integrated on chip, then parallelism and performance increase, but wiring complexity and manufacturing cost increase
Solution Approach 1:
The control logic acts as an intermediary between multiple execution units and the instruction stream. It manages the complexity of coordinating multiple units by centrally analyzing dependencies and directing instructions appropriately, reducing the wiring burden compared to fully interconnected execution units.
4Productivity
If static optimization is applied in multi-threaded or virtualized environments, then single-thread performance improves, but overall system performance deteriorates due to resource competition
Solution Approach 1:
The control logic dynamically analyzes register access conflicts for each instruction pair at runtime, adapting to the actual execution context regardless of threading or virtualization. This dynamic approach maintains single-thread efficiency while being transparent to multi-threaded and virtualized environments, as each thread's instructions are optimized independently based on actual dependencies.
Data Source
AI summary
A processor with multiple execution units for instruction processing is provided. The processor comprises an instruction decode and issue logic and a control logic for resolving register access conflicts between subsequent instructions and a dependency cache, which comprises a receiving logic for receiving an execution unit indicator indicative of the execution unit the instruction is planned to be executed on, a storing logic responsive to the receiving logic for storing the received execution unit indicator, and a retrieving logic responsive to a request from the instruction decode and issue logic for providing the stored execution unit indicator for an instruction. The instruction decode and issue logic is adapted for requesting execution unit indicator for an instruction from the dependency cache and to assign the instruction to one respective of the execution units dependent on the execution unit indicator received from the dependency cache.