[CentOS-devel] info about centos 7 cloud images and no_timer_check

Hello,
I'm playing with an openstack lab environment based on Icehouse on CentOS 7
and nested virtualization.
Some details about the infra.

L0 Host is on Fedora 23: my laptop with ssd disk and 16Gb of ram, using
Qemu/KVM and virt-manager

L1 Host is CentOS 7 with 4Gb of ram and configured with IceHouse rdo repo
(EOL7) (copy host cpu config in virt-manager of Fedora 23) and packstack
allinone

L2 is Centos 7 cloud image configured with 1Gb of ram
CentOS-7-x86_64-GenericCloud.qcow2 download by end of February 2016

I'm able to do all on this L2 guest (eg ssh login with centos user through
key and attch floating ip) but I noticed 2 things:

1) I was not able to boot because the VM always remained stuck at boot at
message:
  ...trying to set up timer as Virtual Wire IRQ...

I found this
https://bugzilla.redhat.com/show_bug.cgi?id=1175502

but actually my VM is nested with kvm
command line run by L1 is:

qemu     31641     1 88 13:36 ?        00:05:47 /usr/libexec/qemu-kvm -name
instance-00000006 -S -machine pc-i440fx-rhel7.0.0,accel=tcg,usb=off -m 1024
-realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid
e0680ada-1fc8-4d7a-829b-ba581a6252ef -smbios type=1,manufacturer=RDO
Project,product=OpenStack
Nova,version=2014.1.5-1.el7.centos,serial=14603773-bb9a-46e3-b333-07e0b68e65ac,uuid=e0680ada-1fc8-4d7a-829b-ba581a6252ef
-no-user-config -nodefaults -chardev
socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-instance-00000006/monitor.sock,server,nowait
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown
-boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive
file=/var/lib/nova/instances/e0680ada-1fc8-4d7a-829b-ba581a6252ef/disk,if=none,id=drive-virtio-disk0,format=qcow2,cache=none
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
-drive
file=/var/lib/nova/instances/e0680ada-1fc8-4d7a-829b-ba581a6252ef/disk.local,if=none,id=drive-virtio-disk1,format=qcow2,cache=none
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk1,id=virtio-disk1
-drive
file=/var/lib/nova/instances/e0680ada-1fc8-4d7a-829b-ba581a6252ef/disk.swap,if=none,id=drive-virtio-disk2,format=qcow2,cache=none
-device
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x6,drive=drive-virtio-disk2,id=virtio-disk2
-netdev tap,fd=27,id=hostnet0 -device
virtio-net-pci,netdev=hostnet0,id=net0,mac=fa:16:3e:c5:ff:fc,bus=pci.0,addr=0x3
-chardev
file,id=charserial0,path=/var/lib/nova/instances/e0680ada-1fc8-4d7a-829b-ba581a6252ef/console.log
-device isa-serial,chardev=charserial0,id=serial0 -chardev
pty,id=charserial1 -device isa-serial,chardev=charserial1,id=serial1
-device usb-tablet,id=input0 -vnc 0.0.0.0:1 -k en-us -vga cirrus -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x7 -msg timestamp=on

I solved the boot problem using extra property for the C7 image:
glance image-update --property kernel_extra_args="no_timer_check"

and now I'm able to boot without problems
Is it ok my approach? In case is it possible to configure the image itself
directly? Or is there any drawback in setting that parameter?

2) Just at first boot the VM uses much cpu because of this process:
 root      3119  2024  4 12:42 ?        00:00:09 /bin/bash /usr/sbin/dracut
--hostonly --hostonly-cmdline --hostonly-i18n -o plymouth dash resume ifcfg
-f /boot/initramfs-3.10.0-327.10.1.el7.x86_64kdump.img
3.10.0-327.10.1.el7.x86_64

What is it? Can I avoid in any way? For about 5-10 minutes my L0 laptop
runs at 80 degrees... ;-)
Is the load normal during that phase due to my resource constraints or is
it in any way caused by the extra setting in 1) ?

Thanks in advance!

Gianluca
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