TSC host kernel message with kvm.git as host kernel and qemu-kvm.git as userspace

TSC host kernel message with kvm.git as host kernel and qemu-kvm.git as userspace

[Lucas Meneghel Rodrigues]

Hi folks, 

I was doing some work at one of our host machines, the one that runs
upstream (Fedora 14, kvm.git as the kernel and qemu-kvm.git as
userspace), and I noticed the kernel message:

kvm: unreliable cycle conversion on adjustable rate TSC
kvm: SMP vm created on host with unstable TSC: guest TSC will not be
reliable

The host being tested in this case was RHEL 5.5 i386. Command line of
the install test:

/usr/local/autotest/tests/kvm/qemu -name 'vm1' -monitor unix:'/tmp/monitor-humanmonitor1-20101021-160403-PrKT',server,nowait -qmp unix:'/tmp/monitor-qmpmonitor1-20101021-160403-PrKT',server,nowait -serial unix:'/tmp/serial-20101021-160403-PrKT',server,nowait -drive file='/tmp/kvm_autotest_root/images/rhel5-32.qcow2',index=0,if=ide,cache=none -device rtl8139,mac=9a:47:46:1a:e6:b9,netdev=idAcPzhW -netdev user,id=idAcPzhW,tftp='/usr/local/autotest/tests/kvm/images/rhel55-32/tftpboot',bootfile='/pxelinux.0',hostfwd=tcp::5000-:22,hostfwd=tcp::5001-:12323 -m 1024 -smp 2 -drive file='/tmp/kvm_autotest_root/isos/linux/RHEL-5.5-i386-DVD.iso',media=cdrom,index=2 -drive file='/tmp/kvm_autotest_root/images/rhel55-32/ks.iso',media=cdrom,index=1 -vnc :0  -boot d -boot cn

I was oriented by Marcelo to report this to the kvm list and copy Zach
on the e-mail. There, done :)

Lucas

Re: TSC host kernel message with kvm.git as host kernel and qemu-kvm.git as userspace

[Zachary Amsden]

On 10/21/2010 09:49 AM, Lucas Meneghel Rodrigues wrote:
> Hi folks,
>
> I was doing some work at one of our host machines, the one that runs
> upstream (Fedora 14, kvm.git as the kernel and qemu-kvm.git as
> userspace), and I noticed the kernel message:
>
> kvm: unreliable cycle conversion on adjustable rate TSC
> kvm: SMP vm created on host with unstable TSC: guest TSC will not be
> reliable
>    

Yes, the message is a warning; without TSC trapping, SMP VMs will have 
unreliable TSC.  In this case, you are advised to use kvmclock or 
another non-TSC clocksource in the guest.

Zach