Offloading Interrupt Load Balancing from SMP Virtual Machines to the Hypervisor

Cloud computing increasingly leverages SMP virtual machines (VMs) to host multi-threaded applications. Interrupt balancing as a problem becomes more challenging because VMs are subject to the hypervisor's scheduling. Since the scheduling delays are typically tens of milliseconds, when they are added to one VM's interrupt delivery, they can seriously degrade the VM's I/O performance. Traditional balancing techniques are designed for dedicated environments, which cannot work well in virtualized environments because VMs are disallowed to directly control the hardware in many cases. In this paper, we present hBalance, a very simple approach to offload interrupt load balancing from SMP-VMs to the hypervisor. To accelerate the interrupt processing, our approach does not require shortening the hypervisor's scheduling time slice, but dynamically redirects interrupts from preempted virtual CPUs to running ones in a balanced manner. hBalance supports both Fully Virtualiized (FV) guests and Para-Virtualized (PV) guests, and exhibits high portability among various hypervisors. With our prototype implementation in Xen, the experimental results with both micro-level and application-level benchmarks show that hBalance significantly improves SMP-VMs' I/O performance while introduces moderate overhead.