Paravirtualization Vs Virtual Containers

This is an interesting study conducted by University of Michigan and HP comparing XEN (paravirtualization) and OpenVZ (virtual containers).

XEN, MS Virtual Server and VMWare all use paravirtualization, while OpenVZ and Virtuozzo use Virtual Containers.

The study reports that response times can increase by 400 to 600% for XEN, even with the host running only a few nodes. This is largely because of the overhead XEN presents.

OpenVZ had a minimal response time increase of around 100% for the same workload. The study also noted that XEN used twice the amount of CPU for the same workload compared to OpenVZ

What the article says is that L2 cache misses (both memory and instruction) signficantly increased in the XEN study. For non Computer Science people, that basically means the processor caching system was far less effective for XEN, compared to OpenVZ (and single OS systems). Caching is important because the time it takes to read instructions or data from RAM is significantly slower than reading instructions from the cache. Cache misses are similar to page-faults (in OS memory architecture).

To a consumer what this means is that Virtual Containers (OpenVZ, Virtuozzo) may offer much better performance than any paravirtualization based solution as long as the host isn't overloading their VPS system.

While paravirtualization offers higher fault-tolerance, in most well designed virtual container based VPS systems, this is minimized and the performance overhead may not be worth it.