Publication: Wrong-Path-Aware Entangling Instruction Prefetcher
Authors
Ros, Alberto
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Publisher
Institute of Electrical and Electronics Engineers
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Description
© 2023.IEEE. This document is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by /4.0/
This document is the Accepted version of a Published Work that appeared in final form in IEEE Transactions on Computers. To access the final edited and published work see DOI 10.1109/TC.2023.3337308
Abstract
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 lowerlevel 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 wrongpath-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.
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