People at vmware have provided patches for RHEL 5 that aim to fix timekeeping issues in vmware guests.

https://bugzilla.redhat.com/show_bug.cgi?id=463573

Description of problem (excerpt) :

"In a virtual environment, timekeeping for RHEL 64 bit kernels can be problematic, since time is kept by counting timer interrupts for this kernel.

The problem arises when the VM is descheduled for some portion of time. When the VM is rescheduled, the hypervisor needs to "catch up" delivering timer interrupts so that the kernel can determine the correct time.

Until the VM is caught up, the kernel's time will be behind, causing short term divergence of the kernel's time with wallclock time. Additionally, under certain overcommitment conditions, it may not be possible for the hypervisor to fully catch up. In this case, the kernel time can fall behind over the long term.

The solution is to change the kernel's timekeeping algorithm to keep time based on how much time has elapsed according to a time counter rather than by counting interrupts. This is similar to the timeofday algorithm used by clocksource enabled mainline kernels or the RHEL5 32bit kernel."

They were hoping to get them into the RHEL 5.3 kernel but unfortunately this is not going to happen. It looks like the patches will be in the RHEL 5.4 kernel. Using the patches provided in the bugzilla, I have rebuilt the latest test kernel (-125) that is available from http://people.redhat.com/dzickus. You can download the patched kernel from:

http://centos.toracat.org/kernel/centos5/vmware463573/

I have test-installed it on a couple of CentOS-5 x86_64 guests. Still too early to say anything about the clock issue, but so far so good. If you get a chance to give it a try, please share what you find.

Thanks,

Akemi (nick: toracat)