RTC problems on Dell Poweredge Servers

Matt Domsch Matt_Domsch at dell.com
Sun Jan 7 23:46:38 CST 2007

On Sun, Jan 07, 2007 at 06:57:28PM -0500, Francis Lessard wrote:
>    Hi !
>    (this is mostly my original post on Howtoforge)
>    I really hope we come to a solution.
>    I have installed a VMWare server on Debien Etch kernel 2.6.18-3-686 on my
>    brand new Poweredge 860. I still have an issue related to RTC.
>    On a standard server (non-dell from what I tested), issuing the command
>    :> hwclock  and then cat /proc/interrupts. The number would increase
>    beside IO-APIC-edge rtc showing that hwclock receives correct interrupts
>    form /dev/rtc...
>    That's not the case on the Dell PowerEdge 860. And after looking through
>    all my Dell Linux installations, they all exibit the same problem, all
>    with different kernels ! (tested on 2 poweredge sc430)
>    The symptom is corrected on Dell servers by adding --directisa option to a
>    hwclock command or in /etc/init.d/hwclock.sh for booting slowdowns and
>    shutdowns... But the this perticular issue is affecting directly VMware
>    server. The vmware server need /dev/rtc for keeping up time correctly. So
>    even though this solves the problem in hwclock, it does not fix my issue.
>    This message is logged in syslog :
>    Jan  3 16:08:41 pe860 kernel: rtc: lost some interrupts at 2048Hz.

doh!  a 2048 Hz RTC is pretty often.  VMware ESX recommends people
running 2.6 kernels to change their timer interrupt from 1000 Hz to
100 Hz exactly because a guest waking up the hypervisor so often is
terribly inefficient and you see big time skews this way.  This is
covered in the VMware documentation pretty well.  Adding a 1000 Hz
clock and a 2048 Hz RTC interrupt is bound to cause the system to
spend a lot of time accounting for time and not much time doing actual

Matt Domsch
Software Architect
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com

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