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This paper introduces a novel technique for emulating double-precision (FP64) general matrix multiplication (DGEMM) using FP8 matrix multiply-accumulate (MMA) units, addressing the challenge of limited FP64 performance gains in modern hardware. The method adapts the Ozaki-II scheme, previously incompatible with FP8, to efficiently leverage FP8 MMA units for DGEMM emulation. Results show a significant reduction in the number of FP8 matrix multiplications compared to FP8-based emulation via the Ozaki-I scheme, enabling more efficient FP64 emulation on new GPU architectures.
Forget slow FP64: this work unlocks efficient double-precision matrix multiplication on modern GPUs by adapting the Ozaki-II scheme to run on faster FP8 hardware.
In high-performance computing (HPC) applications, FP64 arithmetic remains indispensable for ensuring numerical accuracy and stability. However, in recent hardware generations, improvements in FP64 arithmetic performance have been relatively modest. Consequently, achieving sustained performance gains for FP64 computations necessitates the effective utilization of high-throughput low-precision arithmetic, such as INT8 and FP8. In several recent architectures, such as NVIDIA Blackwell Ultra and NVIDIA Rubin, INT8 performance has been significantly reduced, making reliance on INT8 alone insufficient. The use of FP8 arithmetic is thus increasingly important. In this paper, we propose a method for emulating double-precision (FP64) general matrix--matrix multiplication (DGEMM), a fundamental and performance-critical kernel in many HPC applications, using FP8 matrix multiply-accumulate (MMA) units. The Ozaki-I and Ozaki-II schemes are well established as foundational approaches for emulating DGEMM via low-precision arithmetic. For DGEMM emulation via the Ozaki-I scheme, implementations using INT8, FP8, and FP16 MMA units have been proposed, all of which can be realized based on the same underlying algorithmic structure. In contrast, although implementations of DGEMM emulation via the Ozaki-II scheme using INT8 MMA units have been reported, the original algorithm cannot be directly adapted to exploit FP8 MMA units. In this work, we introduce a novel technique to overcome this limitation and demonstrate FP64 matrix multiplication emulation based on the Ozaki-II scheme that operates on FP8 MMA units. Compared to FP8-based emulation via the Ozaki-I scheme, our method significantly reduces the number of required FP8 matrix multiplications and enables efficient FP64 emulation on emerging GPU architectures.
