Shared Instruction Prefetch Pipeline for Multicore Fetch Bandwidth
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Solution Overview
Problem
Existing multicore processing systems face inefficiencies in instruction prefetching due to the high cost of providing private instruction memory for each core and the complexity of full cache coherent solutions, which are impractical for cross-lane processing units (XPUs).
Innovation Solution
A hardware circuit with a shared instruction memory (TiMem) and independent instruction buffers (iBuf) for each core, utilizing a prefetch pipeline architecture that includes a prefetch unit and instruction router to optimize instruction delivery, reducing redundant requests and improving bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If independent instruction streams are fetched for each thread on separate cores, then thread-level parallelism is achieved, but instruction fetch bandwidth is insufficient and performance degrades
Solution Approach 1:
The patent merges the instruction fetch resources of multiple cores into a shared instruction fetch unit. Multiple cores share a common instruction fetch bandwidth pool, allowing coordinated instruction fetching across cores. This resolves the bandwidth insufficiency by combining individual core fetch capabilities into a larger shared resource that can serve multiple threads simultaneously.
Solution Approach 2:
The instruction fetch unit is designed to serve multiple cores universally rather than being dedicated to a single core. The same fetch infrastructure can service instructions for any thread on any core, making the system more efficient at utilizing available bandwidth across diverse thread workloads while maintaining the ability to handle thread-level parallelism.
2Use of energy by moving object
If conservative prefetching is used to avoid misprediction penalties, then fetch resource utilization is improved, but prefetcher performance is limited
Solution Approach 1:
The patent implements feedback mechanisms where the prefetcher monitors actual instruction demand and fetch outcomes. When mispredictions occur or bandwidth is available, the system adjusts prefetching aggressiveness based on observed performance. This feedback loop allows the system to balance between conservative resource usage and aggressive prefetching to maximize overall prefetcher effectiveness without wasting fetch bandwidth.
Data Source
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AI summary
Aspects of the disclosure are directed to methods, systems, and apparatuses using an instruction prefetch pipeline architecture that provides good performance without the complexity of a full cache coherent solution deployed in conventional CPUs. The architecture can include components which can be used to construct an instruction prefetch pipeline, including instruction memory (TiMem), instruction buffer (iBuf), a prefetch unit, and an instruction router.