Cascaded Delayed Execution Pipeline Cache Miss Scheduling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern processors experience pipeline stalls due to cache misses, particularly when data is not readily available in lower cache levels, leading to inefficiency and underutilization of pipelined processor cores.
Innovation Solution
Implementing a cascaded delayed execution pipeline unit with multiple execution pipelines that allow load instructions to be scheduled in the least delayed pipeline, enabling early determination of cache misses and reducing pipeline stalls by initiating higher-level cache or memory access quickly, and reissuing instructions in the most delayed pipeline to align with completed cache access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If instructions are executed in a pipelined manner to increase processing speed, then the number of instructions processed per unit time increases, but pipeline stalls occur when cache misses happen, leading to underutilization of the processor core
Solution Approach 1:
The patent applies preliminary action by executing load instructions in the least delayed pipeline stage before data is actually needed by subsequent instructions. This allows the processor to initiate cache access operations early, determining cache hits or misses before dependent instructions are ready to execute, thereby preventing pipeline stalls and maintaining continuous instruction flow
2Productivity
If multiple execution pipelines are used to process instructions in parallel, then processing throughput increases, but scheduling complexity increases to determine which pipeline executes which instruction
Solution Approach 1:
The patent applies local quality by assigning different characteristics to different pipeline stages - specifically, the least delayed pipeline is designated for executing load instructions while other pipelines handle different instruction types. This localized functional differentiation simplifies the scheduling decision to a rule-based assignment rather than complex optimization, reducing scheduling complexity while maintaining parallel processing throughput
3Reliability
If data is fetched from higher cache levels or memory when a cache miss occurs, then the required data is retrieved, but the pipeline must stall while waiting for data retrieval, reducing processor efficiency
Solution Approach 1:
The patent executes load instructions in the least delayed pipeline to perform preliminary cache access operations before subsequent dependent instructions are ready to execute. This preliminary action determines cache hit/miss status early, allowing the system to initiate data fetching from higher cache levels or memory in advance, so that data is ready when needed and the pipeline continues executing other instructions without stalling
Data Source
AI summary
A method and apparatus for minimizing unscheduled D-cache miss pipeline stalls is provided. In one embodiment, execution of an instruction in a processor is scheduled. The processor may have at least one cascaded delayed execution pipeline unit having two or more execution pipelines that execute instructions in a common issue group in a delayed manner relative to each other. The method includes receiving an issue group of instructions, determining if a first instruction in the issue group is a load instruction, and if so, scheduling the first instruction to be executed in a pipeline in which execution is not delayed with respect to another pipeline in the cascaded delayed execution pipeline unit.