Enabling Dynamic Virtual Frequency Scaling for Virtual Machines in the Cloud

International audienceWith the democratization of the Cloud paradigm, many applications are developed to be executed inside virtual machines hosted by remote data centers providing an Infrastructureas-a-Service (IaaS). These applications, developed by different users with different goals, tend to have different behaviors, hence a similar treatment on the Cloud provider side seems to be sub-optimal. Indeed, VM are black boxes to which are attached vCPUs, whose frequency are all the same, and are mainly indicative. In our opinion, an important limitation can be noted here. Because the Cloud provider is unaware of the applications that are executed inside the VMs, it has little insight on the behavior of the applications, and how to manage the VMs. For these reasons, Cloud provider can assign too much or too few resources to a VM, and might rely on migration mechanism to cope with that problem. In this paper, we propose to attach a virtual frequency to the VM template, which can be configured by the customer to better describe her expected application requirements, and the associated quality of service. Then, to enforce this virtual frequency, we designed a controller that leverages the Linux cgroup system to dynamically adjust the configuration on the host machine. We evaluate our new controller on a real infrastructure with real CPU-intensive applications executed by VM with different frequencies. We also discuss the benefits of our virtual frequency capping for VM placement