I believe each physical host has at least 8 real cores. They give each instance 4 virtual cores. As long as CPU time is available, an instance can use the full capacity of four cores. If there is contention for CPU time, every instance gets an equal share of CPU, which is also their fare share of CPU, because all the instances on a box are the same size/pricepoint. Further, larger instances are shared with a proportionally smaller number of other instances.

My experience, which seems to be shared by just about anyone who has published benchmarks, is that Linode is appropriately conservative on the degree to which they oversell CPU, because generally, it appears that a task that wants 100% of four cores does in fact get close to 100% of four cores.

The only thing to look out for is that there is quite a difference in single threaded performance between their newer hardware and their older hardware. Our app is written in one of the popular interpreted dynamic languages. Generic benchmarks for that language showeda 2-3x difference on some tests when run on the different hardware, and our app showed similar differences on CPU bound tasks.

There are a few implications of this:

First, it complicates things when you try to make your staging environment mirror production. The quick check is to look at /proc/cpuinfo and see if clock,cache and model line up. If not, open a ticket and ask them to migrate instances so things match.

Second, while they try to size things appropriately so that your guaranteed CPU Is the same, regardless of which generation of host you are on, your peak CPU is going to vary dramatically since you get 4 cores, irregardless.

Great - we've got two moderately large (12+ instances) clusters with them, one in the US, one in the UK - both are fast.