Re: early printk timings way off

[Rogier Wolff <R.E.Wolff@BitWizard.nl>]

On Fri, Sep 16, 2005 at 01:00:45AM +0200, Jesper Juhl wrote:
> 
> I'll just dig into it myself for now, but thank you, if I get really
> stuck I may ask him.

The explanation: "jiffies starts at rollover minus a bit" seems to be
spot-on: If jiffies are 32bit, and counting at 1000 per second, the
2^32 / 1000 works out. 

I expect the kernel to run without turning on (timer) interrupts for a
while during boot: It is still initializing things like memory and the
processor. Without those, interrupts won't work. This means that the
timer interrupt will not count in real-time.

A "jump" of 27 seconds seems unlikely, except if somehow the
interrupts are somehow accounted. It could very well be that the
kernel nowadays has a mechanism of measuring the fact that it missed a
timer interrupt and corrects for that. This would mean that around the
"jump", the kernel suddenly realized it missed around 27000 interrupts
and added 27000 to "jiffies"....

I'd say: Would be nice to get the timings right, but not worth the
trouble: There are good technical reasons for the observed facts.

	Roger. 

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