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

[George Anzinger <george@mvista.com>]

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@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml