[jacquesm]

It's not a myth. A VM is effectively a slice of your computer that you can pre-allocate in such a way that that VM can not exceed its boundaries (in theory of course, this works perfectly, in practice not always).

So all other things being equal, if you slice up your machine into 5 equally apportioned segments and you run a user process in one of those 5 slices that tries to hog the whole machine it will only manage to create 1/5th of the load that it would be able to create if it were running directly on the guest OS.

So yes, linux does 'fair slicing' if you can live with the fact that a single process will determine what is fair and what is not. That that process gets pre-empted and that other processes get to run as well does not mean the machine is not now 100% loaded.

Using quota for disk space, 'nice', per-process limits for memory, chroot jails for isolation and so on you can achieve much the same effect but a VM is so much easier to allocate. It does have significant overhead and of course it has (what doesn't) it's own set of issues but resource allocation is actually one of the stronger points of VMs.

[justincormack]

Well yes, but kvm is a vm thats just using Linux to do this vm scheduling. The main issue is that the API for containers is less well defined (IO scheduling is not necessarily fully fair with VMs, but its mainly aio on the host side at least).