Actually, most of our VM are running kernel version 2.6, and are causing little or no problem with clock drift. But thank you for your useful input on the subject - I'll take this into account the next time I come across a drifting clock. On 11/13/08, Eric Sisler <lbylnxgek@xxxxxxxxx> wrote: > > Kenneth Holter <kenneho.ndu@xxxxxxxxx> wrote: > > > What puzzles me is why this VM drifts so much, while most of our other > VMs > > doens't (at least not more than NTPd can handle). > > The Linux 2.6.x kernel is largely the culprit. Are your other VMs 2.4 > kernels? The kernel frequency HZ changed between the 2.4.x & 2.6.x > kernels. A snippet of a *much* earlier posting. Unfortunately I > don't have the name to give credit where it's due: > > "The 2.4 kernels have HZ set to 100, while 2.6 kernels have HZ set to > 1000. This value affects the frequency of clock interrupts that are > generated, and those are per-CPU (that's why the problem gets worse > when you go SMP). This change in frequency is the main reason for the > clock problems for Linux guests. That is why your RH 7.3 works OK, > while RHEL 4 doesn't. Another drawback of this change in value of HZ > is that 2.6 kernels will waste more CPU cycles than 2.4 kernels when > idling. Much more. When you have several SMP Linux 2.6 guests, just > to keep the kernels running will waste a lot of the available CPU time. > > One recommendation from VmWare is to recompile the 2.6 kernel with HZ > reduced back to 100 (as it was in 2.4 kernels). I haven't yet > attempted this, but I heard reports that it works nicely. > > Apperently the behaviour of Windows is much closer to 2.4 Linux > kernels. Hence you don't see the problem that much there." > > As I mentioned earlier, adding a small patch to set the kernel clock > HZ back to 100 & building custom RPMs does work, but can be time > consuming if you have many servers to maintain. I *think* I have notes > about the process somewhere if anyone's interested. > > -Eric > > -- > redhat-list mailing list > unsubscribe mailto:redhat-list-request@xxxxxxxxxx?subject=unsubscribe > https://www.redhat.com/mailman/listinfo/redhat-list > -- redhat-list mailing list unsubscribe mailto:redhat-list-request@xxxxxxxxxx?subject=unsubscribe https://www.redhat.com/mailman/listinfo/redhat-list
