Overhead when enabling hot-add/hot-plug?

[EJimenezNieto]

Hello, I always thought that when you enable cpu-hot plug and memory hot-add, the amount of overhead of the virtual machines becomes the same as if it would have 64 vCPUs and 1TB of RAM:

http://9to5it.com/vmware-hot-add-enable-default/

In Yellow Bricks blog, Duncan states that there is an overhead but is not very explicit where does this extra tax apply:

Enabling Hot-Add by default? /cc @gabvirtualworld

I have tested it myself, and this are my results:

2 vCPU, 4 GB RAM (Hot-add/hot-plug enabled):

4 vCPU, 12 Gb RAM (Hot-add/hot plug enabled):

Of course, not the overhead you expect of a 64 vCPU 1TB monster. Just a normal VM with overhead scalating properly.

Can you bring me more info about this topic? Thank you.

[Shocko]

Hmm. I always though that this was due to the guest. For hot plug to work, the guest must reserve memory space for the maximum amount of memory that could be assigned i.e. the Sytem PTEs increase. Since these are non-paged pool the guest memory consumption increases accordingly.

[felakkad]

Hello,

Old topic but still in times.

I just done the same test as you and i find the same result.

When i switch ON the Hot Add Memomy and CPU i get a normal overhead.

I will write to Duncan linking the threat.