FaReS: Fair Resource Scheduling for VMM-Bypass InfiniBand Devices

In order to address the high performance I/O needs of HPC and enterprise applications, modern interconnection fabrics, such as InfiniBand and more recently, 10GigE, rely on network adapters with RDMA capabilities. In virtualized environments, these types of adapters are configured in a manner that bypasses the hypervisor and allows virtual machines (VMs) direct device access, so that they deliver near-native low-latency/high-bandwidth I/O. One challenge with the bypass approach is that it causes the hypervisor to lose control over VM-device interactions, including the ability to monitor such interactions and to ensure fair resource usage by VMs. Fairness violations, however, permit low-priority VMs to affect the I/O allocations of other higher priority VMs and more geerally, lack of supervision can lead to inefficiencies in the usage of platform resources. This paper describes the FaReS system-level mechanisms for monitoring VMs' usage of bypass I/O devices. Monitoring information acquired with FaReS is then used to adjust VMM-level scheduling in order to improve resource utilization and/or ensure fairness properties across the sets of VMs sharing platform resources. FaReS employs a memory introspection-based tool for asynchronously monitoring VMM-bypass devices, using InfiniBand HCAs as a concrete example. FaReS and its very low overhead (<;1%) monitoring methods are evaluated with microbenchmarks and representative HPC codes running on modern multicore platforms connected via InfiniBand, using the Xen hypervisor. For these codes fairness is achieved within 2% of the required value.