Re: early printk timings way off

[Rogier Wolff]

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. 

-- 
** R.E.Wolff@xxxxxxxxxxxx ** http://www.BitWizard.nl/ ** +31-15-2600998 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
Q: It doesn't work. A: Look buddy, doesn't work is an ambiguous statement. 
Does it sit on the couch all day? Is it unemployed? Please be specific! 
Define 'it' and what it isn't doing. --------- Adapted from lxrbot FAQ
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/