Ok, so we found a "solution" that I thought I'll share in case this thread pops up in a future search.
The problem was that our Redhat 5.x guests still run with a kernel that lacks the "tickeless" feature, meaning that they are poking the host a 1000 times per second even if they haven't anything to do. Disabling hyperthreading and most importantly, adding the parameter "divider=10" to the kernel boot line in grub does indeed lower the cpu utilization in the hosts almost to 0% when idling. In our case we use the command sudo /sbin/grubby --update-kernel=ALL --args="divider=10" To upgrade the /boot/grub/grub.conf file and then we restart the vm. Thank you everyone for the help. Xavier On Mon, Nov 10, 2014 at 8:32 AM, Xavier Naveira <[email protected]> wrote: > We tried a minimal installation from CD of RedHat 5.10 and it is the same. > > This should be fairly easy to reproduce: > > - Install a RedHat 6.5 hypervisor > - Install a RedHat 5.10 guest in it > - Enjoy your overused CPU > > Is there someone with a similar setup out there? > > Xavier > > On Fri, Nov 7, 2014 at 12:30 PM, Gianluca Cecchi < > [email protected]> wrote: > >> On Fri, Nov 7, 2014 at 10:48 AM, Xavier Naveira <[email protected]> >> wrote: >> >>> Hi, >>> >>> We have installed and added a new hypervisor into the ovirt cluster but >>> this time with disabled HT. >>> >>> I migrated a RedHat 5.10 machine to it and immediately the qemu-kvm >>> process running the vm (freshly installed, just basic packages) began to >>> consume 20-40% CPU as showed running top on the hypervisor. >>> >>> Now that I have a hypervisor to run tests in, what would you suggest the >>> next step is? >>> >>> Thank you. >>> >>> Xavier >>> >>> >>> >> If I remember correctly you had to test plain Qemu/KVM on CentOS 6.5 and >> see if the difference is made by oVirt itself or by the OS changed from 5.x >> to 6.y... >> And also compare command line (eventually both in 5.x and 6.x) between >> plain Qemu/KVM and oVirt spawned VMs >> Gianluca >> > >
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