arXiv AI

BlockLock: Reproducible LLM Inference with Fixed Batch Geometry

arXiv Machine Learning
Sep 14

Dissecting GPU Utilization for LLM Inference on Nvidia Hopper

The paper investigates how a single SM utilization metric can misrepresent the true workload of large language model (LLM) inference on Nvidia Hopper GPUs. By profiling vLLM with FlashAttention‑3 and cuBLASLt on an H100 NVL across various phases (cold prefill, warm prefill, and decode) and varying sequence length and batch size, the authors replace the single utilization figure with eight detailed counter‑validated views. These views, tied to specific Nsight Compute counters or formulas, reveal how factors such as fragment fill, occupancy limits, stall signatures, wave quantization, and kernel selection create utilization gaps across four production models and six per‑layer kernel roles.

By Mohammad Siavashi, Gerald Q. Maguire Jr., Dejan Kostic, Marco Chiesa
arXiv Machine Learning
Sep 23

Accelerating the Mitigation of LLM Inference Nondeterminism Across GPU Architectures

The paper addresses the problem of non‑deterministic outputs from large language models (LLMs) when run on different GPU architectures, caused by floating‑point non‑associativity and hardware‑dependent kernel choices. It proposes a set of fixed‑configuration fused‑upcast GEMM kernels that load 16‑bit weights, upcast to FP32, and perform IEEE‑754 compliant reductions in a problem‑shape‑dependent order, ensuring identical linear‑layer outputs across NVIDIA Ampere, Ada, and Hopper GPUs. The new approach achieves 1.17–3.1× faster end‑to‑end performance than existing solutions and halves weight‑memory traffic while maintaining cross‑architecture reproducibility.

By Liam Cooper, Shinnung Jeong, Hyeran Jeon, Jeffrey Young, Hyesoon Kim
arXiv AI
Oct 1

Decode-Latency Feedback Prefill: A Model-Free Controller and Its Generalization Limits

The paper introduces Decode‑Latency Feedback Prefill (DLFP), a model‑free controller that adjusts prefill chunk sizes during concurrent autoregressive inference to reduce interference between new and ongoing requests. Implemented in vLLM, DLFP achieves significant reductions in P99 inter‑token latency on Qwen3‑0.6B while maintaining output correctness and SLO compliance, though it fails to generalize to larger models or multi‑GPU setups. The study highlights the limits of this approach and suggests the need for a completion‑timed controller for broader applicability.

By Gaurav Agarwal, Ashish Garg, Isha Singhal
arXiv Machine Learning
Oct 28

DualPace: Decoupled Scheduling and Cooperative GPU--CPU Decoding for LLM Serving

DualPace is an LLM serving runtime that decouples scheduling between a GPU engine and an AMX‑enabled CPU engine, allowing the CPU to independently batch and advance decodes while still cooperating with the GPU for dense stages. This design expands key‑value cache capacity into host memory and reduces bursty CPU progress, leading to significant throughput gains—up to 43.2 % over NEO and 90.6 % over vLLM—without increasing latency. The system also maintains low time‑to‑first‑token and supports higher request rates at comparable tail latency.

By YuXuan Lin, KeQiang Wu, Kingsum Chow
arXiv Machine Learning
Oct 12

Taking Tokenization off the Host for Agentic LLM Serving

The paper introduces GraphTok, a GPU-based tokenizer that executes the entire tokenization pipeline as a single CUDA graph, matching reference token IDs for models such as GPT‑2, Llama 3, Qwen 2.5, DeepSeek‑V3, and Gemma 3. GraphTok achieves significant speedups, encoding one million GPT‑2 tokens in 1.7–3.2 ms and outperforming the leading CPU tokenizer gigatoken by 4.7–6.0× on Llama 3. In a vLLM deployment with cached prefixes, it reduces mean time‑to‑first‑token by 2.1–2.4× and dramatically increases request throughput, sustaining 518 req/s of 121k‑token traffic versus 296 with gigatoken.

By Mohammad Siavashi, Pascal Schwinte, Ali Banaei, Gerald Q. Maguire Jr., Marco Chiesa, Dejan Kosti\'c
arXiv Machine Learning
Oct 23

Amplifying Latency and Cost of LLM Inference via Rowhammer Attack

The paper introduces LLVMhammer, a Rowhammer attack that induces a bit‑flip in Triton’s MLIR/LLVM compilation pipeline, causing the generation of a suboptimal GPU kernel that persists across inference runs. A single successful bit‑flip can increase LLM inference latency by 4–16 % on NVIDIA RTX 4090 and AMD RX 7900 XTX GPUs, and can also degrade output quality, lowering BERTScore to as low as 25 %. The attack is GPU‑vendor‑agnostic and demonstrates that memory corruption in the compiler can have lasting performance and security impacts on large‑language‑model inference.

By Mrityunjay Shukla, Shubham Roy, Biswabandan Panda