Questions on VM creation

Submitted by ghomem on Fri, 04/12/2013 - 12:43

Hi,

I have a couple of doubts on VM creation:

  1. docs says VMs are created with 1GB of disk space. However we can choose to allocate more on the VM creation GUI. Is it possible to reserve space for the machine while not allocating it at the moment, like in VMWare?

  2. What does "cores per socket" mean? I read that the number of VCPUs is the number of physical cores that the VM will be able to use on the physical host. I don't see what the "cores per socket" means. Could be the info on the physical host number of cores per socket, but then why would it be stored on a per-VM basis?

Thanks Gustavo

Status: 
Closed (fixed)

Comments

Submitted by ghomem on Fri, 04/12/2013 - 12:45

I tried to look at the Help section but it is missing for KVM:

Failed to read help file /usr/libexec/webmin/server-manager/help/newkvm.html

Submitted by JamieCameron on Fri, 04/12/2013 - 13:13

  1. No, there is no way to reserve space for a VM. You would need to allocate it all up-front.

  2. Cores per socket sets the number of CPU cores per physical CPU, as seen by the VM.

I will fix that missing help page in the next release.

Submitted by ghomem on Fri, 04/12/2013 - 13:20

I created a VM from your Ubuntu 12.04 KVM template, that had 15 VCPUs (and 1 core per socket - to be clarified) in the configuration.

In the end, it gets created with only 8 VCPUs

root@vdi01:~# cat /proc/cpuinfo |grep processor |wc -l 8 root@vdi01:~#

Is there a limit?

Plus, are there Ubuntu 12.04 x64 templates for KVM? (can't find them at New System Images).

Thanks Gustavo

Submitted by ghomem on Fri, 04/12/2013 - 13:27

But I'm using Ubuntu 12.04 from you! My question is for x64, ie 64bits, images.

Submitted by ghomem on Fri, 04/12/2013 - 13:30

Regarding the VCPUs, what is written in the link you've sent is

Max. Virtual CPUs per Guest 64

It says 64, not 8.

Submitted by ghomem on Fri, 04/12/2013 - 13:35

I now changed the options on "System Resources" to

6 VCPUs 2 cores per socket

So I should see 12 entries in /proc/cpuinfo of the guest system. However, I was left with 6 entries only.

There seems to be a problem here.

Submitted by JamieCameron on Fri, 04/12/2013 - 14:24

Oops, you are right .. I was looking at the max number of virtual network interfaces.

What if you change it to 12 VCPUs, with 2 cores per socket?

Actually, I don't see much gain from setting the number of cores per socket to anything other than 1.

Submitted by ghomem on Fri, 04/12/2013 - 16:46

It seems that whatever is put in "cores per socket" is ignored and whatever is put at VCPUs is truncated to 8.

We purchased a Cloudmin Pro license to implement a large terminal server, so we need this problem sorted out. Plus, we predict the same scenario to be repeated further times.

So, we kindly request a solution from your side.

Note: the "cores per socket" is important for windows guests, since you can bypass the physical socket limit for certain windows versions and increase parallelism by increasing the number of cores.

Submitted by JamieCameron on Fri, 04/12/2013 - 17:15

Could you login to the host system for this VM and post the full command line for the kvm process for the VM? I'd like to see what parameters Cloudmin is passing to the KVM process.

Submitted by ghomem on Sat, 04/13/2013 - 05:14

For 12 VCPUs and 2 cores per socket:

/usr/libexec/qemu-kvm -name vdi01.XXXX -m 8192 -drive file=/home/virtual/VM/vdi01.XXXXX.img,media=disk,index=0,if=virtio,boot=on -boot c -net tap,vlan=0,script=/home/virtual/VM/vdi01.XXXX-eth0.sh -net nic,vlan=0,macaddr=02:54:00:72:2E:15,model=virtio -vnc :1,password -usbdevice tablet -monitor tcp:127.0.0.1:40000,server -smp 12,cores=2

Submitted by JamieCameron on Sat, 04/13/2013 - 11:51

You may be running into a compiled-in limit in the linux kernel on the number of cores recognized.

Check /boot/grub/grub.conf on the VM, and see if the maxcpus= parameter is set on the kernel line. If it is missing, try adding maxcpus=16 to increase the limit.

I'd also be interested to see the output from dmesg on the VM.

Submitted by ghomem on Sat, 04/13/2013 - 12:19

Seems that Ubuntu 12.04 has a limit on 8 CPUs , for 32 bits :( Are you planning to release a 64 bit Cloudmin template image?

http://askubuntu.com/questions/158555/how-many-maximum-cpus-does-ubuntu-...

From dmesg:

[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 8 reached. Processor 8/0x8 ignored. [ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 8 reached. Processor 9/0x9 ignored. [ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 8 reached. Processor 10/0xa ignored. [ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 8 reached. Processor 11/0xb ignored.

Submitted by JamieCameron on Sat, 04/13/2013 - 13:28

You may be able to adjust that by compiling a custom kernel - according to http://oreilly.com/linux/excerpts/9780596100797/kernel-configuration-opt... the NR_CPUS param is the one you want to adjust.

We don't have any immediate plans to release 64-bit images - but you can create your own by installing Ubuntu 12.04 into an empty VM. For docs on this, see http://www.virtualmin.com/documentation/cloudmin/virtualization/empty