Out-of-Order Instruction Scheduling for Critical Path Latency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing out-of-order processors struggle to identify the critical path of instruction execution efficiently, leading to suboptimal performance due to latency issues on the critical path, while optimizations on non-critical paths have minimal impact.
Innovation Solution
Implementing criticality detection circuitry that sparsely assigns tokens to instructions to track distances and predict critical instructions, allowing for prioritization in scheduling and cache retention policies to reduce latency on the critical path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If out-of-order processors issue the oldest ready instruction operation each cycle, then instruction execution is simplified, but latency on the critical path cannot be reduced
Solution Approach 1:
The system performs preliminary analysis of instruction dependencies and critical paths before execution begins. By identifying critical instructions in advance and pre-loading them into the reservation station, the processor can ensure they are executed without delay once the critical path is recognized, thereby reducing latency without complicating the execution process
Solution Approach 2:
The system continuously monitors instruction execution and updates its understanding of critical paths based on actual runtime behavior. This feedback mechanism allows the processor to adapt its scheduling decisions dynamically, identifying and prioritizing critical instructions as they become apparent during execution while maintaining simple issue-order processing
2Productivity
If the critical path is identified through token-passing algorithms, then critical instructions can be prioritized, but hardware area and power consumption increase
Solution Approach 1:
The system extracts only the essential information needed for critical path identification from the full instruction stream. Instead of implementing complete token-passing algorithms that track every dependency, the processor selectively monitors and records only the critical dependency relationships, reducing hardware requirements while maintaining prioritization capability
Solution Approach 2:
The system implements a partial version of critical path analysis that focuses only on the most important dependencies. By using a simplified approach that records critical path information in a compact format within the reservation station, the processor achieves sufficient prioritization without the full hardware overhead of complete token-passing algorithms
3Measurement precision
If all instructions are tracked for critical path identification, then accuracy is improved, but power consumption increases
Solution Approach 1:
The system applies different levels of tracking to different instructions based on their importance. Critical instructions that lie on or may lie on the critical path receive full tracking and prioritization, while non-critical instructions are processed with minimal overhead. This selective approach maintains high accuracy for critical path identification without the energy cost of tracking every instruction uniformly
Data Source
AI summary
Techniques are disclosed relating to critical path identification and prioritization. In some embodiments, criticality detection circuitry is configured to sparsely assign tokens to a subset of instructions to be executed by pipeline circuitry, track a distance between execution of the instruction and execution of one or more instructions that depend on the instruction, and train instructions as predicted-critical or not based on tracked distances. In some embodiments, scheduling circuitry is configured to prioritize predicted-critical instructions over other instructions for issuance.