  Many emerging AI applications request distributed machine learning (ML) among
edge systems (e.g., IoT devices and PCs at the edge of the Internet), where
data cannot be uploaded to a central venue for model training, due to their
large volumes and/or security/privacy concerns. Edge devices are intrinsically
heterogeneous in computing capacity, posing significant challenges to parameter
synchronization for parallel training with the parameter server (PS)
architecture. This paper proposes ADSP, a parameter synchronization scheme for
distributed machine learning (ML) with heterogeneous edge systems. Eliminating
the significant waiting time occurring with existing parameter synchronization
models, the core idea of ADSP is to let faster edge devices continue training,
while committing their model updates at strategically decided intervals. We
design algorithms that decide time points for each worker to commit its model
update, and ensure not only global model convergence but also faster
convergence. Our testbed implementation and experiments show that ADSP
outperforms existing parameter synchronization models significantly in terms of
ML model convergence time, scalability and adaptability to large heterogeneity.
