[ntp:questions] Re: ntp sanity limit kills ntp daily

Richard B. Gilbert rgilbert88 at comcast.net
Wed Jun 15 11:23:41 UTC 2005

Brad Knowles wrote:

> At 11:24 AM -0400 2005-06-14, Richard B. Gilbert wrote:
>>  They do spend the $2 and there is a quartz crystal installed.  You 
>> don't
>>  get much for $2 these days but it's not THAT bad!
>     Actually, it frequently is that bad.  But that's only part of the 
> problem.
Not bad enough to lose 1200 seconds during backups!!

>>  The problem is not in the hardware but in the software.
>     There are problems with the quartz crystal oscillators.  There are 
> BIOS problems.  There are ACPI/APIC problems.  Those can all be lumped 
> into the "hardware problems" category, although some of them may be 
> able to be fixed with an update to the BIOS, changing the ACPI or APIC 
> configuration, etc....
>>                                                            The clock we
>>  are talking about is the software clock maintained by the O/S.
>     The OS and the application fall into the "software problems" 
> category.  Again, some of them can be fixed, and others are not 
> practical to fix (i.e., it may not be possible to replace the OS with 
> something else and still run the necessary applications in the way the 
> customer wants).
>>  Most, or all, versions of Windows and Linux exhibit this problem!
>>  Other operating systems; e.g. BSD and Solaris, do not.
>     The hardware problems are shared by all OSes using that same 
> hardware platform.
>     The software problems are unique to a given OS platform and the 
> software running on that platform.  Unfortunately, as shipped by the 
> respective vendors, Linux frequently has more software problems in 
> this area than other OSes, but those should be able to be corrected by 
> generating a new kernel image with corrected value.  For Windows, 
> there's little you can do to fix the underlying problems at the OS level.
Changing 1000 Hz to 100 Hz in the Linux Kernel does not fix the problem, 
it merely reduces the number of lost interrupts by ~90%.  Losing only 
120 seconds during backups instead of 1200 is just not that big a win!

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