Edge computing can avoid long network transmission delay, thus reducing the task response time. However, edge servers cannot respond quickly to massive computing requests due to limited computing power, which may lead to long queuing delays, thus failing to meet low latency requirements of delay-sensitive Internet of Things (IoT) applications. Furthermore, the per-computing-unit energy consumption in edge computing is much higher than that in cloud computing. This article studies the edge–cloud collaborative computing for energy efficiency while meeting the delay requirements of IoT applications in mobile edge computing systems. We formulate the energy efficient computation offloading problem for mixed tasks, including divisible and indivisible tasks. We theoretically analyze the relationship between delay guarantee and energy consumption in edge–cloud collaborative environment. We further analyze the system stability based on Lyapunov stability theory. Then, an energy efficient and delay guaranteed edge–cloud collaborative computation offloading algorithm is proposed to provide delay guarantee for delay-sensitive IoT applications while minimizing the energy consumption of the edge–cloud computing system. Theoretical analysis and experimental results show that, compared with the benchmark algorithms, our algorithm can provide strict delay guarantee for stringent-delay-sensitive IoT applications, and low delay for soft-delay-sensitive IoT applications, while consuming lower energy.

Task scheduling is key to performance optimization and resource management in cloud computing systems. Because of its complexity, it has been defined as an NP problem. We introduce an online scheme to solve the problem of task scheduling under a dynamic load in the cloud environment. After analyzing the process, we propose a server level agreement constraint adaptive online task scheduling algorithm based on double deep Q-learning (SLA-DQTS) to reduce the makespan, cost, and average overdue time under the constraints of virtual machine (VM) resources and deadlines. In the algorithm, we prevent the change of the model input dimension with the number of VMs by taking the Gaussian distribution of related parameters as a part of the state space. Through the design of the reward function, the model can be optimized for different goals and task loads. We evaluate the performance of the algorithm by comparing it with three heuristic algorithms (Min-Min, random, and round robin) under different loads. The results show that the algorithm in this paper can achieve similar or better results than the comparison algorithms at a lower cost.