On Wed, Sep 17, 2008 at 1:35 PM, Akemi Yagi <amyagi at gmail.com> wrote: > On Wed, Sep 17, 2008 at 11:23 AM, Jeff <jlar310 at 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. Our experience with HZ=100 in 4.6 kernels was nearly perfect time sync, at least to within a second over one week. Not so with divider=10. I will grab the -78 SRPM and give it a spin. -- Jeff