On Wed, Sep 17, 2008 at 11:23 AM, Jeff jlar310@gmail.com wrote:
Under 4.6, we recompiled the kernel with HZ=100 for improved time-keeping in VMware guests. I've read about the backporting of the divider patch into RHEL/CentOS 4.7, but it sounds like it also comes with some bugs. I have been unable to determine the current status of the divider option in the latest 4.7 kernel update. I have experimented with "divider=10" and it works with no major problems, except that the guest clock drifts ahead very slightly. So far, it looks like several seconds of drift per day. Not a show-stopper, but still a concern. With HZ=100, our time sync was spot on. In both cases we are using "clock=pit nosmp noapic" and tools.syncTime="TRUE". If it matters, our host machines are CentOS 4.6 x86_64.
Can anyone comment on the current status of bugs with the divider option? Is anyone getting accurate time sync with divider=10 with 2.6.9-78.0.1? Is there anything else to watch out for? Is there any fix for the slight time drift with divider=10?
I am primarily concerned with i686.
Currently, the SRPM for -78.0.1 is missing from the mirrors, so if I want to update, I have to rely on the divider option for my VMware guests. It also appears that Tru has not yet added any -78 RPMs to his kernel-vm project.
As far as I can tell from my limited experience, the clock issue occurs regardless of the method taken, namely, kernel-vm (100Hz kernel) or divider=10. (Of course, this is with older kernels, not -78) Both options work fine when it comes to idle %cpu. One improvement of the 4.7 kernel is that it does not crash even when divider= is used together with clock=pit like it does with CentOS-5 kernels.
Yes, the srpm file for -78.0.1 is missing (see http://bugs.centos.org/view.php?id=3132 ). But we can try -78 for performing a test.
Akemi