FTDS: Adjusting Virtual Computing Resources in Threshing Cases

In a virtual execution environment, dynamic computing resource adjustment technique, configuring the computing resource of virtual machines automatically according to the actual loads generated by applications, is often adopted in virtual machine monitor to improve the resource utilization rate. Traditionally, the simple Additive Increase Subtractive Decrease (AISD) scheme is used as an adjusting rule. However, in some special situations, for example, compiling kernel in a virtual machine, the configuration of virtual machines may change abruptly because of the violent vibration of workload during a short interval, and the threshing can inevitably result in additional overhead under AISD rule. In this paper, we extend the Proportional-Integral-Derivative (PID) algorithm and present a feedback control model for configuring virtual computing resources, and propose an innovative adjusting scheme called Forecasting and Time Delayed Subtraction (FTDS) to reduce the overhead caused by threshing. The FTDS uses both statistic history of resource requests and current utilization of computing resource to predict whether threshing happens and to determine how many and when to adjust the amount of virtual CPUs. Experimental results show that FTDS can effectively reduce the jitter occurred in adjusting and make the performance penalty for threshing decreased from 9% to 0.3% compared with AISD, while maintaining that in non-threshing cases the same as AISD.