Instruction Prefetching via Processor Trace Data
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Solution Overview
Problem
Current instruction cache prefetching methods are ineffective due to lack of support in common instruction set architectures, high implementation costs, and poor performance, especially in low-latency servers, where instruction cache misses are less common and data pipeline optimization hampers instruction prefetching.
Innovation Solution
A system and method for prefetching instructions using processor trace data to determine and prefetch instruction addresses and stack ranges during idle time, employing transactional execution and out-of-order execution to prevent incorrect cache entries and improve prefetch order, enabling universal CPU cache warming for critical code execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If pre-execution technique is used for instruction cache prefetching, then critical code can be accessed faster from cache, but the technique occupies processors for long periods of time and delays processing of new input in low latency applications
Solution Approach 1:
The system performs preliminary analysis of execution traces to identify critical code regions that should be prefetched into cache, then executes prefetching operations during idle time rather than blocking the processor, thus preparing cache entries in advance without occupying the processor for long periods
Solution Approach 2:
The system automatically monitors processor activity, identifies idle periods, and autonomously performs prefetching operations during these idle times without requiring external control or blocking the main execution path, allowing the system to serve its own cache warming needs without impacting low-latency processing
2Reliability
If instruction cache prefetching is implemented using conventional methods, then cache miss performance may improve, but the implementation cost is high and effectiveness is limited due to lack of architecture support
Solution Approach 1:
The system uses a universal prefetching mechanism that works across different instruction set architectures without requiring architecture-specific modifications, leveraging existing processor features like idle time detection and cache management to achieve portable instruction prefetching functionality
Solution Approach 2:
The system introduces an intermediary layer that monitors processor execution, identifies critical code regions through trace analysis, and manages prefetching operations independently of the core instruction execution path, thereby reducing the complexity burden on the main processor architecture
3Reliability
If pre-execution cache warming is performed, then instruction cache hits increase, but incorrect cache warming code can cause errors, crashes, or hangs in the program
Solution Approach 1:
The system performs partial prefetching by identifying and prefetching only the critical portions of code that are most likely to be executed, rather than attempting to prefetch entire programs or uncertain code regions, thus reducing the risk of introducing incorrect cache entries that could cause errors
Solution Approach 2:
The system uses execution trace feedback to continuously monitor which code regions are actually executed and adjust prefetching decisions accordingly, validating that prefetched code is correct and relevant before committing it to cache, thereby preventing incorrect cache warming code from causing crashes
Data Source
AI summary
Systems and methods for prefetching instructions and data run a program in a test environment, execute a tracing application on the program to collect processor trace data, use the processor trace data to extract a plurality of instruction addresses and a single continuous stack range to be prefetched during a run-time of the program, at initialization of the program, load the extracted plurality of instruction addresses and the extracted stack range, relocate the plurality of extracted instruction addresses and the extracted stack range into the program, and at run-time, prefetch one or more of the plurality of extracted instruction addresses and the extracted stack range during idle time of the program.