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.
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
On Wed, Sep 17, 2008 at 1:35 PM, Akemi Yagi amyagi@gmail.com wrote:
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.
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.
On Wed, Sep 17, 2008 at 11:56 AM, Jeff jlar310@gmail.com wrote:
On Wed, Sep 17, 2008 at 1:35 PM, Akemi Yagi amyagi@gmail.com wrote:
On Wed, Sep 17, 2008 at 11:23 AM, Jeff jlar310@gmail.com wrote:
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.
That is very interesting. This is the first time I've heard about the difference between the two with regard to timekeeping problems. Please keep us informed of your testing.
Akemi
On Wed, Sep 17, 2008 at 12:15 PM, Akemi Yagi amyagi@gmail.com wrote:
On Wed, Sep 17, 2008 at 11:56 AM, Jeff jlar310@gmail.com wrote:
On Wed, Sep 17, 2008 at 1:35 PM, Akemi Yagi amyagi@gmail.com wrote:
On Wed, Sep 17, 2008 at 11:23 AM, Jeff jlar310@gmail.com wrote:
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.
That is very interesting. This is the first time I've heard about the difference between the two with regard to timekeeping problems. Please keep us informed of your testing.
Just wanted to let you (and anyone who is interested) know that Tru has kindly offered kernel-vm for -78 and -78.0.1 in his usual place:
http://people.centos.org/tru/kernel-vm/4/
Akemi
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Akemi Yagi -
Jeff