Deterministic replay, which provides the ability to travel backward in time and reconstruct the past execution flow of a multiprocessor system, has many prominent applications. Prior research in this area can be classified into two categories: hardware-only schemes and software-only schemes. While hardware-only schemes deliver high performance, they require significant modifications to the existing hardware. In contrast, software-only schemes work on commodity hardware, but suffer from excessive performance overhead and huge logs. In this article, we present the design and implementation of a novel system, Samsara, which uses the hardware-assisted virtualization (HAV) extensions to achieve efficient deterministic replay without requiring any hardware modification. Unlike prior software schemes which trace every single memory access to record interleaving, Samsara leverages HAV on commodity processors to track the read-set and write-set for implementing a chunk-based recording scheme in software. By doing so, we avoid all memory access detections, which is a major source of overhead in prior works. Evaluation results show that compared with prior software-only schemes, Samsara significantly reduces the log file size to 1/70th on average, and further reduces the recording overhead from about 10x, reported by state-of-the-art works, to 2.1x on average.

In virtualized environments, the customers who purchase virtual machines (VMs) from a third-party cloud would expect that their VMs run in an isolated manner. However, the performance of a VM can be negatively affected by co-resident VMs. In this paper, we propose vExplorer, a distributed VM I/O performance measurement and analysis framework, where one can use a set of representative I/O operations to identify the I/O scheduling characteristics within a hypervisor; and potentially leverage this knowledge to carry out I/O based performance attacks to slow down the execution of the target VMs. We evaluate our prototype on both Xen and VMware platforms with four server benchmarks and show that vExplorer is practical and effective. We also conduct similar tests on Amazon's EC2 platform and successfully slow down the performance of target VMs.