FPnew: An Open-Source Multiformat Floating-Point Unit Architecture for Energy-Proportional Transprecision Computing
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2021-04
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Journal Article
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Abstract
The slowdown of Moore's law and the power wall necessitates a shift toward finely tunable precision (a.k.a. transprecision) computing to reduce energy footprint. Hence, we need circuits capable of performing floating-point operations on a wide range of precisions with high energy proportionality. We present FPnew, a highly configurable open-source transprecision floating-point unit (TP-FPU), capable of supporting a wide range of standard and custom FP formats. To demonstrate the flexibility and efficiency of FPnew in general-purpose processor architectures, we extend the RISC-V ISA with operations on half-precision, bfloat16, and an 8-bit FP format, as well as SIMD vectors and multiformat operations. Integrated into a 32-bit RISC-V core, our TP-FPU can speedup the execution of mixed-precision applications by 1.67x with respect to an FP32 baseline, while maintaining end-to-end precision and reducing system energy by 37%. We also integrate FPnew into a 64-bit RISC-V core, supporting five FP formats on scalars or 2, 4, or 8-way SIMD vectors. For this core, we measured the silicon manufactured in Globalfoundries 22FDX technology across a wide voltage range from 0.45 to 1.2 V. The unit achieves leading-edge measured energy efficiencies between 178 Gflop/sW (on FP64) and 2.95 Tflop/sW (on 8-bit mini-floats), and a performance between 3.2 and 25.3 Gflop/s. © 2020 IEEE.
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published
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Volume
29 (4)
Pages / Article No.
774 - 787
Publisher
IEEE
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Software
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Subject
Energyefficient; floating-point unit; multiformat; RISC-V; transprecision computing
Organisational unit
03996 - Benini, Luca / Benini, Luca
Notes
Funding
732631 - Open Transprecision Computing (EC)