  Deep neural networks (DNNs) have been widely adopted for various mobile
inference tasks, yet their ever-increasing computational demands are hindering
their deployment on resource-constrained mobile devices. Hybrid deep learning
partitions a DNN into two parts and deploys them across the mobile device and a
server, aiming to reduce inference latency or prolong battery life of mobile
devices. However, such partitioning produces (non-uniform) DNN fragments which
are hard to serve efficiently on the server.This paper presents Graft -- an
efficient inference serving system for hybrid deep learning with latency
service-level objective (SLO) guarantees. Our main insight is to mitigate the
non-uniformity by a core concept called DNN re-alignment, allowing multiple
heterogeneous DNN fragments to be restructured to share layers. To fully
exploit the potential of DNN re-alignment, Graft employs fine-grained GPU
resource sharing. Based on that, we propose efficient algorithms for merging,
grouping, and re-aligning DNN fragments to maximize request batching
opportunities, minimizing resource consumption while guaranteeing the inference
latency SLO. We implement a Graft prototype and perform extensive experiments
with five types of widely used DNNs and real-world network traces. Our results
show that Graft improves resource efficiency by up to 70% compared with the
state-of-the-art inference serving systems.
