Abstract—Provisioning strategies relying on CPU load may be suboptimal for many applications, be-cause the relation between CPU load and application performance can be non-linear and complex. With the knowledge of the relation between CPU load and application performance, resource provisioning strate-gies could be tuned to a particular application, but the required knowledge is difficut to obtain, because classic benchmarking is not suited for performance evaluation of partial-load scenarios. As a remedy, we present Showstopper, a tool capable of achieving and sustaining a predefined partial CPU load (or replay a load trace) by controlling the execution of arbitrary CPU-bound workloads. By analyzing performance in-terference among applications running in colocated virtual machines, we demonstrate how Showstopper enables systematic and reproducible exploration of the platform- and application-specific relation between CPU load and application performance. I.