Optimization Of Network I/O On Xen

There are two main branches in the field of Virtualization technology. One is Full-virtualization and another is Para-virtualization. Para-virtualization based on Xen has been deployed widely which includes three important understructures: virtualization of CPU, RAM and I/O device. Virtualization of I/O device can be implemented by three different models, Virtual device model, Simulating device model and Direct model. In the three of them, Virtual device model has taken obvious advantage.In the Virtual device model, virtual machine drives network device as virtual network device. The driver program has a front-end driver and a back-end driver. Xen provides various low-level mechanisms to support the driver program, such as I/O ring, memory sharing and event channel.There are two factors for network performance, bandwidth and responsibility. This paper focuses on bandwidth. Xen allocates bandwidth resource among virtual machines by a policy based on Credit value algorism. The algorism focuses on fairness, security and isolation. The Credit value indicates the bandwidth of corresponding virtual machine. When a packet is sent, the Credit of corresponding virtual network device will be reduced by the same size. If the Credit is not enough, a timer will be set. Allocating period and the allocated Credit implement control on bandwidth resource. However, the policy lacks of flexibility in some complex scenarios.First, the Credit value can obtain from configuration file only when the virtual machine starts. And the Credit value can't be adjusted when the corresponding virtual machine is running. Obviously, that lacks of flexibility. This paper posted an optimized policy by analyzing the current policy and the principle of Xen virtual network device implementation.Secondly, the optimized policy can provide QoS service and make the Credit value can be adjusted when virtual machine is running. This paper also posts a method to detect whether the virtual NIC is busy or not.Second, bandwidth of a Virtual NIC can't beyond the bandwidth of corresponding physical NIC that limits the abstraction and virtualization for bandwidth resource. A solution was posted in this paper to address the problem by binding several physical NICs.Third, Xen is using Credit value to manage bandwidth. When some virtual machines are set to provide stream service , such as online video and ftp, Xen can not fix the request. Xen can not provide a QoS service for virtual machine. This paper addressed this by a optimized policy. A mechanism to indicating virtual NIC is busy or not was posted. So the bandwidth could be allocated among virtual machines.This paper addressed the three questions above without any additional resource consumed.