  Performance isolation is a keystone for SLO guarantees with shared resources
in cloud and datacenter environments. To meet SLO requirements, the state of
the art relies on hardware QoS support (e.g., Intel RDT) to allocate shared
resources such as last-level caches and memory bandwidth for co-located
latency-critical applications. As a result, the number of latency-critical
applications that can be deployed on a physical machine is bounded by the
hardware allocation capability. Unfortunately, such hardware capability is very
limited. For example, Intel Xeon E5 v3 processors support at most four
partitions for last-level caches, i.e., at most four applications can have
dedicated resource allocation. This paper discusses the feasibility and
unexplored challenges of providing SLO guarantees beyond the limits of hardware
capability. We present CoCo to show the feasibility and the benefits. CoCo
schedules applications to time-share interference-free partitions as a
transparent software layer. Our evaluation shows that CoCo outperforms
non-partitioned and round-robin approaches by up to 9x and 1.2x.
