Loop Fetch Circuit to Reduce Processor Pipeline Flushes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Pipeline flushes caused by loop instructions lead to computational inefficiencies, increased power consumption, and decreased processor performance due to the need to repeatedly execute branch instructions and flush the pipeline, especially when using branch predictors.
Innovation Solution
A processor is equipped with a loop instruction fetch and execution circuit that detects loops during the instruction fetch stage, storing loop iteration data in registers, and updates this data based on execution-stage determinations to minimize pipeline flushes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If branch instructions are used to control loop execution, then program flow control is achieved, but pipeline flushes occur causing performance degradation
Solution Approach 1:
The patent applies preliminary action by detecting loop instructions during the instruction fetch stage and pre-calculating the number of iterations before the loop executes. This allows the pipeline to be pre-configured with the correct number of iterations, eliminating the need for repeated pipeline flushes during loop execution and thereby resolving the performance degradation caused by branch instructions.
Solution Approach 2:
The patent introduces an intermediary mechanism by adding a loop detection circuit and iteration counter that acts as a mediator between the instruction fetch unit and the execution unit. This intermediary structure enables the system to track loop iterations independently, allowing the pipeline to maintain correct instruction flow without frequent flushes, thus improving processor performance while maintaining flow control capability.
2Productivity
If the pipeline size is increased to improve processing throughput, then more instructions can be processed simultaneously, but the number of invalid instructions fetched and decoded increases
Solution Approach 1:
The patent applies feedback by implementing a loop detection mechanism that monitors the instruction stream and provides feedback about loop iterations to the instruction fetch unit. This feedback allows the system to dynamically adjust the number of instructions fetched and decoded, ensuring that the pipeline is filled with valid instructions only, thereby reducing energy waste from processing invalid instructions while maintaining high throughput.
3Productivity
If branch predictors are used to reduce pipeline flushes, then computational efficiency improves, but device complexity increases
Solution Approach 1:
The patent applies the extraction principle by removing the complex branch prediction mechanism from the processor architecture and replacing it with a simpler loop detection and iteration counting system. This extraction eliminates the need for sophisticated branch predictors while achieving similar or better performance by directly tracking loop iterations through dedicated hardware circuits, thereby reducing device complexity.
Data Source
AI summary
Embodiments of the technology described herein include hardware of a processor configured to decrease the number of pipeline flushes caused by loop instructions by extracting data regarding the loop during the instruction fetch stage of the instruction cycle of the processor and/or updating the data as determined during the execution stage of the instruction cycle of the processor. In this regard, the control unit of the processor can direct the instruction fetch unit of the processor to fetch instructions of the loops based on the number of iterations of the loop as stored in a register associated with the instruction fetch stage of the processor. In this manner, certain computing devices employing embodiments of the technology described herein decrease the number of pipeline flushes, thereby increasing computational efficiency and hardware lifespan compared to using conventional technology.