[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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