Code Prefetch Instruction for Lower Fetch Latency
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Solution Overview
Problem
The latency of fetching data from memory in computer systems decreases performance, and existing prefetching techniques for data can lead to cache pollution and self-modifying code scenarios.
Innovation Solution
Implementing a code prefetch instruction in the instruction set architecture (ISA) to prefetch code to the instruction cache and/or instruction translation lookaside buffer, allowing execution at the fetch stage of the pipeline instead of the execute stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If data prefetching techniques are used to move data from main system memory to cache, then the time required to fetch data is reduced, but cache pollution and self-modifying code scenarios occur
Solution Approach 1:
The patent segments the memory hierarchy into separate instruction cache and data cache structures. By implementing distinct prefetch mechanisms for instructions (using instruction cache) versus data (using data cache), the system avoids the cache pollution problem that occurs when data prefetching techniques are applied to code, while still enabling effective prefetching for both purposes simultaneously.
2Productivity
If code is fetched during the execute stage, then instruction execution can proceed, but the latency increases and performance decreases
Solution Approach 1:
The patent implements code prefetching that retrieves instructions during the fetch stage of the pipeline, performing the prefetch action before the execute stage begins. This preliminary fetching of instructions into the instruction cache eliminates the latency penalty during execution, allowing the processor to maintain high throughput without waiting for memory access during the critical execute phase.
Data Source
AI summary
Embodiments of apparatuses, methods, and systems for code prefetching are described. In an embodiment, an apparatus includes an instruction decoder, load circuitry, and execution circuitry. The instruction decoder is to decode a code prefetch instruction. The code prefetch instruction is to specify a first instruction to be prefetched. The load circuitry to prefetch the first instruction in response to the decoded code prefetch instruction. The execution circuitry is to execute the first instruction at a fetch stage of a pipeline.