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SubjectRe: [PATCH] HZ==100 assumptions

Steve Underwood writes:
>"Albert D. Cahalan" wrote:
>> Eric Lammerts writes:
>>> On Wed, 28 Jul 1999, Riley Williams wrote:
>>
>>>> However, the standard used by MSDOS (which I assume is what you're
>>>> referring to) is for the clock to tick ~18.2 times per second (to
>>>> be more accurate, 65536 ticks per hour), in which case the correct
>>>
>>> This is incorrect. The BIOS/MSDOS clock is generated from a 14.31818MHz
>>> crystal clock divided by 12 * 65536.
>>
>> Nope. Clock frequency varies. Originally it was related to a standard
>> video frequency. More recent computers use a frequency designed to make
>> DOS timekeeping be more accurate. (the 65536 ticks/hour I suppose)
>
> Nope. Many modern computers use an el. cheapo clock that is just plain
> inaccurate, and they don't keep time very well. Any Compaq ProLiant produced

I didn't say anything about the _quality_ of the clock. Quality is
unrelated to the intended frequency.

When running without an external reference, how should Linux keep time?
The kernel can assume that a video reference is used, or it can assume
that the system was designed for DOS timekeeping. The kernel can't do
anything about an unstable or out-of-spec clock, but it can at least
start with an estimate that is appropriate for common modern hardware.



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