text: virtualization - HyperV - low CPU usage - Super User
  I have a server that is only used as a host for virtual machines. OS is windows server 2008 R2 and it is running on 16 CPU and 48 GBs of RAM.
  On aforementioned server there are 8 VMs, each having 4 CPUs and 4 GBs of RAM. On those VMs we are running some CPU intensive tasks. Each machine has nearly 100% cpu usage. After I noticed slow performance I went to the host machine and started playing with process explorer. It turned out that cpu usage is very low. Also I/O is very low, and of course, memory consumption is high, which is expected.
  Of course, I don't expect that those 4 virtual cores dedicated to a VM work as fast as real, hardware 4 cores, but still I expected a higher consumption of real hardware. Is this sort of behaviour normal? I see that the most of CPU usage on host machine are marked as interrupts (which I guess is normal) and all those interrupts are passed to only one core (which is strange). Are there out of box optimization that I could perform to finally use all that processing power that is under the hood.
  My knowledge of virtualization technology is near to embarrassing, so I would be grateful for any links that could enlightened me :)
  virtualization windows-server-2008-r2 hyper-v share|improve this question asked Mar 21 '12 at 17:23
  You have 16 cores trying to handle the load of 32 virtual cores. How many threads are trying to run? By the sound of it you have more threads then you have cores to handle them. It's fine to give vms more cores then you actually have if you don't intend to max out all vms at all times. This is probably also what is causing all the interrupts as things like keyboard and mouse have to preform an interrupt to get CPU time.
  Also as a new(er) user to virtualization try to keep the resources you allocate mirrored to the resources you physically have available. After you understand your hyper-visor platform better you can then branch out into over allocating your resources. I wish I could help more but I have limited experience with hyper-v.
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