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At-the-Roofline Sparse Tensor Contractions on Vector Processors for Transformer Inference

Bowen Wang, Chi Zhang, Diyou Shen, Renzo Andri 2026-07-30
Isa Extension Roofline Codesign × Compiler Runtime HPC Sparsity

The problem is that fine-grained sparsity in Transformer inference cannot be efficiently exploited on vector processors because existing RVV architectures lack native support for Gustavson's dataflow, forcing reliance on software index decoding and L1-backed indexed memory operations that keep sparse tensor contractions far below the roofline bound. The method introduces Ventaglio, a runtime-configurable sparse execution unit with RVV ISA extensions that provides indexed gather-accumulate-scatter support to drive sparse tensor contractions toward their roofline performance. Experimental evidence from a 12nm FinFET implementation shows Ventaglio accelerates sparse tensor contraction kernels by 6.9–7.4× over optimized RVV baselines with only 3.1% area overhead, and on a DuoGPT-pruned LLaMA-3-8B model with 40–60% dual sparsity achieves 2.40–5.25× and 2.06–3.16× speedup over dense baselines during prefill and autoregressive decoding, respectively. This matters because it demonstrates that hardware-software co-design can close the roofline gap for sparse tensor contractions, enabling practical speedups for Transformer inference on vector processors without prohibitive area cost.

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Beyond Prefill-Decode Disaggregation: Dissecting LLM Inference for Heterogeneous Platforms via Dynamic Operator Scheduling

Jiaqi Yang, Jiayi Li, Yihan Fu, Hongxiao Zhao 2026-07-30
Hardware Roofline Codesign × Compiler Runtime HPC LLM Inference

The problem is that prefill-decode disaggregation and roofline-based operator placement are insufficient for partitioning LLM inference across heterogeneous systems due to workload shape, device contention, and weight layout constraints. DOPS is a hardware-aware, closed-loop framework that uses a stage-aware DAG, a Bifocal scheduler for dynamic operator placement, and a Weight Layout Arbiter (WLA) for selecting efficient weight layouts. On heterogeneous platforms combining NPUs and PIM devices, Bifocal achieves geometric-mean speedups of 1.20× to 2.23× over the PD baseline, with WLA adding 1.28× to 1.33× further speedup. This matters because DOPS enables systematic analysis of workload sensitivity and hardware scalability, improving LLM serving efficiency on diverse heterogeneous hardware.

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