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Wrong-Path-Aware Entangling Instruction Prefetcher
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DOI：10.1109/TC.2023.3337308.png)
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Abstract
En 中文
Instruction prefetching is instrumental for guaranteeing a high flow of instructions through the processor front end for applications whose working set does not fit in the lower-level caches. Examples of such applications are server workloads, whose instruction footprints are constantly growing. There are two main techniques to mitigate this problem: fetch directed prefetching (or decoupled front end) and instruction cache (L1I) prefetching. This work extends the state-of-the-art Entangling prefetcher to avoid training during wrong-path execution. Our Entangling wrong-path-aware prefetcher is equipped with microarchitectural techniques that eliminate more than 99% of wrong-path pollution, thus reaching 98.9% of the performance of an ideal wrong-path-aware solution. Next, we propose two microarchitectural optimizations able to further increase performance benefits by 1.8%, on average. All this is achieved with just 304 bytes. Finally, we study the interplay between the L1I prefetcher and a decoupled front end. Our analysis shows that due to pollution caused by wrong-path instructions, the degree of decoupling cannot be increased unlimitedly without negative effects on the energy-delay product (EDP). Furthermore, the closer to ideal is the L1I prefetcher, the less decoupling is required. For example, our Entangling prefetcher reaches an optimal EDP with a decoupling degree of 64 instructions.
Keywords:
Instruction prefetching
processor front-end
performance
energy efficiency
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