1. In a system that includes a host computing machine and an Single Root I/O Virtualization (SR IOV) storage adapter in which the host machine hosts a virtual machine having a guest operating system (guest) and a virtualization intermediary, a method to coalesce a virtual interrupt responsive to a IO completion on a direct passthrough IOV data path comprising: generating an IO request by the guest; providing a shared memory space in which the guest and the virtualization intermediary share IO completion state information; wherein only the virtualization writes first state information to the shared memory space and the guest reads the first state information from the shared memory space; wherein only the guest writes second state information to the shared memory space and the virtualization intermediary reads the second state variable from the shared memory space; making virtual interrupt coalescing determinations by the virtualization intermediary based upon the shared state information in the shared memory space.