Re: [PATCH] Re: boot time, process start time, and NOW time

[George Anzinger]

Tim Schmielau wrote:
> On Mon, 30 Aug 2004, john stultz wrote:
>
>
> > On Mon, 2004-08-30 at 16:00, Tim Schmielau wrote:
> >
> > > George, please excuse my lack of understanding. What again where the
> > > precise reasons to have an ntp-corrected uptime?
> >
> > Ah, here's the thread with the first mention of it that I could find.
> >
> > http://www.uwsg.iu.edu/hypermail/linux/kernel/0306.1/1471.html

As I recall the problem was that jiffies since boot was being converted to get 
uptime base on 1/HZ = 1 jiffie.  Since it is really not quite that, there was an 
error.  Using clock_monotonic seemed like the right answer as it eliminated the 
error AND made the result consistant with get_clock(CLOCK_MONOTONIC,..).

The alternate answer is, of course, to directly convert the elapsed jiffies. 
The main problem with this is that this can be a BIG number and, therefor, the 
math needs to be carefully.  And, of course, it is inconsistant with 
get_clock(), but that is a new interface...

George
> Ah, it seems George indeed did the patch because of these problems:
>
>   http://www.uwsg.iu.edu/hypermail/linux/kernel/0306.1/1641.html
>
> However, the actual reason were just missing wall_to_monotonic 
> initializations:
>
>   http://www.uwsg.iu.edu/hypermail/linux/kernel/0306.2/1330.html
>
> This was fixed in mainline:
>
>   http://linus.bkbits.net:8080/linux-2.5/cset%403f0e60dcpIosK3b5_uJ-aD9Mare17w
>
> Tim

--
George Anzinger   george@xxxxxxxxxx
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

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