Processor Pipeline Dynamic Delay Assignment
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Solution Overview
Problem
In-order processors face inefficiencies in handling latency between dependent instructions, as they either stall other instructions or require inflexible separate pipelines, which can lead to suboptimal instruction throughput.
Innovation Solution
Implementing a dynamic delay assignment and dynamic functional unit placement mechanism within the processor pipeline to manage latency, allowing instructions to issue in-order while providing flexibility in execution stages by delaying dependent instructions based on the latency of preceding instructions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If instructions are issued in-order through a single pipeline, then simplicity and power efficiency are maintained, but instruction throughput is reduced due to latency stalling
Solution Approach 1:
The patent implements dynamic delay assignment where instructions are assigned delay values based on their dependency latency requirements. The issue circuitry dynamically determines which instructions can be issued in each clock cycle by analyzing assigned delays, allowing the pipeline to adapt its instruction flow dynamically rather than using fixed in-order or fixed out-of-order execution. This resolves the contradiction by introducing controlled flexibility that improves throughput without requiring full out-of-order execution complexity.
Solution Approach 2:
The patent segments the instruction stream by assigning different delay values to different instructions based on their dependency relationships. Instructions are divided into groups that can be issued in parallel when their delays permit, rather than processing them as a single sequential stream. This segmentation allows multiple instructions to progress through the pipeline simultaneously, improving throughput while maintaining manageable complexity through structured organization.
2Loss of time
If separate pipelines are used to handle dependent instructions, then latency is managed, but device complexity and power consumption increase
Solution Approach 1:
The patent makes a single pipeline multi-functional by enabling it to handle both independent and dependent instructions simultaneously through dynamic delay assignment. The same pipeline resources execute instructions with different delay requirements, eliminating the need for separate dedicated pipelines for different instruction types. This resolves the contradiction by achieving the functionality of multiple specialized pipelines through a single universal pipeline structure.
Solution Approach 2:
The pipeline transitions from static in-order execution to dynamic execution where instruction progression is adjusted based on real-time dependency analysis. The issue circuitry dynamically selects which instructions to issue each cycle based on assigned delays, allowing the pipeline to optimize its own instruction flow without requiring separate fixed pipelines. This dynamic adaptation reduces execution time while avoiding the complexity of multiple static pipeline structures.
3Reliability
If instructions are delayed to account for latency, then correct execution order is maintained, but instruction throughput decreases
Solution Approach 1:
The patent applies preliminary action by assigning delay values to instructions before they are issued to the execution pipeline. The issue circuitry analyzes dependency relationships in advance and pre-determines the appropriate delay for each instruction, allowing instructions to be issued in an optimized sequence that maintains correctness while maximizing throughput. This pre-planning resolves the contradiction by ensuring correct execution order is established beforehand, enabling parallel issuance of independent instructions.
Solution Approach 2:
The patent implements feedback through the issue circuitry that monitors assigned delays and adjusts instruction issuance accordingly. The system continuously evaluates which instructions can be issued in the current clock cycle based on their delay assignments and the current pipeline state, creating a feedback loop that optimizes throughput while maintaining correctness. This feedback mechanism resolves the contradiction by dynamically balancing delay requirements against throughput opportunities.
Data Source
AI summary
Executing instructions in a processor includes analyzing operations to be performed by instructions, including: determining a latency associated with a first operation to be performed by a first instruction, determining a second operation to be performed by a second instruction, where a result of the second operation depends on a result of the first operation, and assigning a value to the second instruction corresponding to the determined latency associated with the first operation. One or more instructions are selected to be issued together in the same clock cycle of the processor from among instructions whose operations have been analyzed, the selected instructions occurring consecutively according to a program order. A start of execution of the second instruction is delayed by a particular number of clock cycles after the clock cycle in which the second instruction is issued according to the value assigned to the second instruction.