On Tue, May 27, 2008 at 3:33 PM, Ruslan Sivak <russ at vshift.com> wrote: > Akemi Yagi wrote: >> >> On Tue, May 27, 2008 at 1:07 PM, Tom Bishop <bishoptf at gmail.com> wrote: >> >>> OK, so I need to bring up a new vm and was wondering what the state of vm >>> kernels for centos. I have read this >>> http://bugs.centos.org/view.php?id=2189 >>> about the tick divider but it wasn't clear what the best step forward is >>> for >>> centos 5.1 was, i usually ran with the clocksource=pit option and it >>> looked >>> like that and the divider option caused a problem. I have in the past >>> compiled my own but was wondering what others were now doing, thanks in >>> advance 8-) >>> >> >> Thanks to Tru, kernel-vm is all up-to-date and you can find it here: >> >> http://people.centos.org/tru/kernel-vm/ >> >> and yes, using the clocksource=pit option should not be an issue with >> these kernels. >> >> Akemi > > So if I understand this correctly, one should not be using a stock kernel > when running inside a vm, but should use the kernel-vm kernel? > > Russ You *can* run the distro kernel inside a vm. The CentOS bug entry referred to by the original poster explains in great details why a kernel with 100hz clock rate (kernel-vm) gives you improved performance compared to the distro standard kernel (1000hz) and handles clock drifts better. Recent distro kernels offer a new kernel option "divider=" that lets you reduce the clock rate. This should eventually eliminate the need for the kernel-vm. However, at the moment, the divider= option has a bug that causes problems when it is combined with clocksource=pit. And the timer "pit" is often used when the system clock tends to go faster. Akemi