PSLO: enforcing the X^th percentile latency and throughput SLOs for consolidated VM storage

It is desirable but challenging to simultaneously support latency SLO at a pre-defined percentile, i.e., the X^th percentile latency SLO, and throughput SLO for consolidated VM storage. Ensuring the X^th percentile latency contributes to accurately differentiating service levels in the metric of the application-level latency SLO compliance, especially for the application built on multiple VMs. However, the X^th percentile latency SLO and throughput SLO enforcement are the opposite sides of the same coin due to the conflicting requirements for the level of IO concurrency. To address this challenge, this paper proposes PSLO, a framework supporting the X^th percentile latency and throughput SLOs under consolidated VM environment by precisely coordinating the level of IO concurrency and arrival rate for each VM issue queue. It is noted that PSLO can take full advantage of the available IO capacity allowed by SLO constraints to improve throughput or reduce latency with the best effort. We design and implement a PSLO prototype in the real VM consolidation environment created by Xen. Our extensive trace-driven prototype evaluation shows that our system is able to optimize the X^th percentile latency and throughput for consolidated VMs under SLO constraints.