On Fri, 29 Jul 2016 11:30:00 +0100 "Chathura M. Sarathchandra Magurawalage" <77.chath...@gmail.com> wrote:
> Hi, > > Does anyone know the reason for, VM resizing time to increase faster if you > continuously increase CPU or DISK resources by +1 (e.g. 1-2, 2-3, 3-4, 4-5). > Whereas, when you increase from 1 to any other (e.g. 1-2, 1-2, 1,3, 1-4, 1-5) > it takes less time in comparison. Can anyone give an explanation for this? I > have plotted two graphs. > > https://www.dropbox.com/s/5e8xrrctu0rcwx3/CPU%20scaling%20%20-%20continuous%20vs%20increasing%20from%201.png?dl=0 > https://www.dropbox.com/s/txpkb8k6mpyexv8/CPU%20scaling%20-%20increase%20from%201.png?dl=0 > > The first graph shows the VM CPU resize time (y axis) vs number of vCPUs (x > axis) of continuous (blue) and resize from a VM with 1 vCPU (green) > scenarios.The second graph shows the VM CPU resize time (y axis) vs number of > vCPUs (x axis), when resized from a VM with 1 vCPU at each step (The green > line in first graph). The error bars show the standard error of the gathered > values at each step, as I did resize multiple times to get a mean value. I > use openstack on x86 with KVM, although I have asked the openstack community > I could not yet find an answer to this. > > Thanks! > QEMU can add CPUs only by one CPU object at a time so from QEMU's point of view time of hotplugging a CPU more or less constant. I'd look farther up the stack for issue. CCing Peter, who might look at it from libvirt perspective.
