Mengxin Zheng | Search arXiv

arXiv2026

AgentServeSim: Serving-System Simulation and Policy Search for LLM Agent Programs

Large language model agents execute programs comprising multiple model turns interleaved with external tool calls. Their job completion time depends on how the serving system retains KV state across tool gaps, routes successor turns, and schedules competing programs. Most existing serving simulators operate on request streams in which arrivals are externally supplied and KV state follows request- or cache-scoped semantics. They therefore cannot jointly represent the cross-turn state and policy-dependent successor releases needed to evaluate counterfactual agent-serving trajectories. We present AgentServeSim, a simulator whose unit of execution is the agent program. A Program Control Block maintains cross-turn state, while a Program Orchestrator causally releases successor turns from simulated predecessor completions. A Retention Plane controls KV state across tool gaps, and a Dispatch Plane determines where and when each ready turn executes. We validate AgentServeSim against real vLLM deployments in 20 paired simulator-real cells spanning two GPU platforms, Llama-3.1-8B and Llama-3.1-70B, coding and function-calling agents, and five arrival rates. Mean JCT error remains within 5.5% on B200 and 5.2% in the saturated RTX PRO 6000 regime. Finally, we propose LLM-driven automated agent-serving policy search using AgentServeSim as a CPU-based fitness evaluator. The resulting policies improve mean JCT over hand-written seed policies by 0.5% for KV retention and 2.8% for scheduling.

cs.CL↗

arXiv2026

RPP: A Certified Poisoned-Sample Detection Framework for Backdoor Attacks under Dataset Imbalance

Deep neural networks are highly susceptible to backdoor attacks, yet most defense methods to date rely on balanced data, overlooking the pervasive class imbalance in real-world scenarios that can amplify backdoor threats. This paper presents the first in-depth investigation of how the dataset imbalance amplifies backdoor vulnerability, showing that (i) the imbalance induces a majority-class bias that increases susceptibility and (ii) conventional defenses degrade significantly as the imbalance grows. To address this, we propose Randomized Probability Perturbation (RPP), a certified poisoned-sample detection framework that operates in a black-box setting using only model output probabilities. For any inspected sample, RPP determines whether the input has been backdoor-manipulated, while offering provable within-domain detectability guarantees and a probabilistic upper bound on the false positive rate. Extensive experiments on five benchmarks (MNIST, SVHN, CIFAR-10, TinyImageNet and ImageNet10) covering 10 backdoor attacks and 12 baseline defenses show that RPP achieves significantly higher detection accuracy than state-of-the-art defenses, particularly under dataset imbalance. RPP establishes a theoretical and practical foundation for defending against backdoor attacks in real-world environments with imbalanced data.

cs.CR↗