A Comprehensive Implementation and Evaluation of Direct Interrupt Delivery

As the performance overhead associated with CPU and memory virtualization becomes largely negligible, research efforts are directed toward reducing the I/O virtualization overhead, which mainly comes from two sources: DMA set-up and payload copy, and interrupt delivery. The advent of SRIOV and MRIOV effectively reduces the DMA-related virtualization overhead to a minimum. Therefore, the last battleground for minimizing virtualization overhead is how to directly deliver every interrupt to its target VM without involving the hypervisor. This paper describes the design, implementation, and evaluation of a KVM-based direct interrupt delivery system called DID. DID delivers interrupts from SRIOV devices, virtual devices, and timers to their target VMs directly, completely avoiding VM exits. Moreover, DID does not require any modifications to the VM's operating system and preserves the correct priority among interrupts in all cases. We demonstrate that DID reduces the number of VM exits by a factor of 100 for I/O-intensive workloads, decreases the interrupt invocation latency by 80%, and improves the throughput of a VM running Memcached by a factor of 3.