vBalance: using interrupt load balance to improve I/O performance for SMP virtual machines

Abstract

A Symmetric MultiProcessing (SMP) virtual machine (VM) enables users to take advantage of a multiprocessor infrastructure in supporting scalable job throughput and request responsiveness. It is known that hypervisor scheduling activities can heavily degrade a VM’s I/O performance, as the scheduling latencies of the virtual CPU (vCPU) eventually translates into the processing delays of the VM’s I/O events. As for a UniProcessor (UP) VM, since all its interrupts are bound to the only vCPU, it completely relies on the hypervisor’s help to shorten I/O processing delays, making the hypervisor increasingly complicated. Regarding SMP-VMs, most researches ignore the fact that the problem can be greatly mitigated at the level of guest OS, instead of imposing all scheduling pressure on the hypervisor. In this paper, we present vBalance, a cross-layer software solution to substantially improve the I/O performance for SMP-VMs. Under the principle of keeping hypervisor scheduler’s simplicity and efficiency, vBalance only requires very limited help in the hypervisor layer. In the guest OS, vBalance can dynamically and adaptively migrate the interrupts from a preempted vCPU to a running one, and hence avoids interrupt processing delays. The prototype of vBalance is implemented in Xen 4.1.2 hypervisor, with Linux 3.2.2 as the guest. The evaluation results of both micro-level and application-level benchmarks prove the effectiveness and lightweightness of our solution.