Solution to 100% CPU Usage by Linux Guest on VMWare Fusion

As part of my testing setup, I have an Intel Mac Pro with Mac OS X 10.6 Server (which runs with the 64-bit kernel) on which I run VMWare Fusion 3.0.1 and several Red Hat virtual machines.

I noticed that even at idle, each VM was taking up a high amount (like 100%!) of a CPU core. Additionally, on one VM top was displaying in near-real-time, which was kind of neat but I doubt the intended behavior. Because of this, I suspected the time management in the kernel was off.

Sure enough, Timekeeping Best Practices for Linux Guests has some hints, and for more information than you'll ever want, try Timekeeping in VMWare Virtual Machines (I was particularly interested in the Clocksource Kernels section).

Making the following modification to /etc/grub.conf on RHEL5 brought my CPU usage down from 100% to barely noticeable:

Before:

kernel /vmlinuz-2.6.18-164.11.1.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet

After:

kernel /vmlinuz-2.6.18-164.11.1.el5 ro root=/dev/VolGroup00/LogVol00 rhgb divider=10

I took out quiet because I like to see what's happening when the system boots.

The Note on RHEL 5.4 or CentOS and divider=10 mentions that you do not need this for RHEL 5.4 for accurate timekeeping, but you do need it to prevent the excessive CPU use.

I also modified /etc/ntp.conf as described in the above article, adding

tinker panic 0

to the top of the file and commenting out the following lines:

My VMs are down from 100 percent CPU use to practically zero. Think of the energy savings!