SLOpt: Serving Real-Time Inference Pipeline With Strict Latency Constraint

The rise of machine learning as a service (MLaaS) has driven the demand for complex and customized real-time inference tasks, often requiring cascading multiple deep neural network (DNN) models into inference pipelines. However, these pipelines pose significant challenges due to scheduling complexity, particularly in maintaining strict latency service level objectives (SLOs). Existing systems serve pipelines with model-independent scheduling policies, which ignore the unique workload characteristics introduced by model cascading in the inference pipeline, leading to SLO violations and resource inefficiencies. In this paper, we propose that the serving system should exploit the model-cascading nature and intermodel workload dependency of the inference pipeline to ensure strict latency SLO cost-effectively. Based on this, we design and implement SLOpt, a serving system optimized for real-time inference pipelines with a three-stage codesign of workload estimation, resource provisioning, and request execution. SLOpt proposes cascade workload estimation and ahead-of-time tuning, which together address the challenge of cascade blocking and head-of-line blocking in workload estimation and resource provisioning. SLOpt further implements an adaptive batch drop policy to mitigate latency amplification issues within the pipeline. These innovations enable SLOpt to reduce the 99th percentile latency (P99 latency) by $1.4$ to $2.5$ times compared to the state of the arts while lowering serving costs by up to $29\%$. Moreover, to achieve comparable P99 latency, SLOpt requires up to $70\%$ less cost than existing systems. Extensive evaluations on a 64-GPU cluster demonstrate SLOpt's effectiveness in meeting strict P99 latency SLOs under diverse real-world workloads.