Virtualization and Benchmarking
The old phrase, ‘what cannot be measured cannot be improved’ is a favorite amongst those in the computer industry – and it contains more than a kernel of truth.  That logic has been behind the establishment of a variety of industry organizations, such as SPEC and TPC, which seek to establish standard benchmarks for various workloads.
Virtualization is certainly one of the trendiest technologies and ripe for measurement.  The latest announcements of CPUs from Intel and AMD have all explicitly mentioned and showcased improvements in virtualization performance, along with a flurry of feature names like VPID, Pacifica, Nested Page Tables and Extended Page Tables.  Most of these I’ve described in prior article, but to summarize, a lot of these features are about shifting the burden of virtualization from software (that is, the VMM) onto the hardware by making some hardware operations more complete.  Take for example, THE VPID in Nehalem (incidentally AMD has had an equivalent feature for a while), which reduces transition times between VMs by about a third (compared to the prior generation Penryn).  While it’s great that VM transitions are faster, it’s really hard for an average user to understand what that really means in terms of virtualization performance. Read More »
