Potential and methods for embedding dynamic offloading decisions into application code. (October 2016)

• Record Type: Journal Article
• Authors: Vaz, Gavin; Riebler, Heinrich; Kenter, Tobias; Plessl, Christian
• Is Part Of: Computers & electrical engineering. Volume 55(2016)
• Page Start: 91
• Page End: 111
• Publication Date: 2016-10
• Subjects: Runtime system -- Runtime decision -- Hotspot offloading -- Convey HC-1 -- LLVM -- SCEV; Computer engineering -- Periodicals; Electrical engineering -- Periodicals; Electrical engineering -- Data processing -- Periodicals; Ordinateurs -- Conception et construction -- Périodiques; Électrotechnique -- Périodiques; Électrotechnique -- Informatique -- Périodiques; Computer engineering; Electrical engineering; Electrical engineering -- Data processing; Periodicals; Electronic journals; 621.302854
• DOI: 10.1016/j.compeleceng.2016.04.021
• Languages: English
• ISSNs: 0045-7906

Abstract

Graphical abstract: Abstract: A broad spectrum of applications can be accelerated by offloading computation intensive parts to reconfigurable hardware. However, to achieve speedups, the number of loop iterations (trip count) needs to be sufficiently large to amortize offloading overheads. Trip counts are frequently not known at compile time, but only at runtime just before entering a loop. Therefore, we propose to generate code for both the CPU and the coprocessor, and defer the offloading decision to the application runtime. We demonstrate how a toolflow, based on the LLVM compiler framework, can automatically embed dynamic offloading decisions into the application code. We perform in-depth static and dynamic analysis of popular benchmarks, which confirm the general potential of such an approach. We also propose to optimize the offloading process by decoupling the runtime decision from the loop execution (decision slack). The feasibility of our approach is demonstrated by a toolflow that automatically identifies suitable data-parallel loops and generates code for the FPGA coprocessor of a Convey HC-1. We evaluate the integrated toolflow with representative loops executed for different input data sizes.