Hardware translation coherence for virtualized systems

To improve system performance, operating systems (OSes) often undertake activities that require modification of virtual-to-physical address translations. For example, the OS may migrate data between physical pages to manage heterogeneous memory devices. We refer to such activities as page remappings. Unfortunately, page remappings are expensive. We show that a big part of this cost arises from address translation coherence, particularly on systems employing virtualization. In response, we propose hardware translation invalidation and coherence or HATRIC, a readily implementable hardware mechanism to piggyback translation coherence atop existing cache coherence protocols. We perform detailed studies using KVM-based virtualization, showing that HATRIC achieves up to 30% performance and 10% energy benefits, for per-CPU area overheads of 0.2%. We also quantify HATRIC's benefits on systems running Xen and find up to 33% performance improvements.