Timekeeping [Was: Re: cvs commit: src/usr.bin/vmstat vmstat.c src/usr.bin/w w.c]

[Bruce Evans]

On Fri, 21 Oct 2005, Poul-Henning Kamp wrote:

> In message <20051022011020.T5554 at delplex.bde.org>, Bruce Evans writes:
>
>> How do you resync laptops after suspending them for long enough for
>> the clock to drift?  Use ntpd and let it step, or use ntpd -x and let
>> it take hours to resync?  The right thing to do is step the clocks to
>> the current time immediately so that they are correct while the system
>> is actually being used.
>
> Ahh, and now we get into interesting territory:  What _is_ the
> definition of uptime for a laptop which has been suspended ?
>
> No matter which way you turn, there are dragons...

>> I certainly care about errors of 1 microsecond (although I don't need
>> to), and just remembered that I use stepping to fix up the clock after
>> sitting in ddb with the clock stopped.  This reduces the error in the
>> real time clock to ~1 microsecond per second stopped, but gives an error
>> of 1 second per second stopped in the monotonic time and the boot time.
>> Here the correct treatment is to jump the monotonic time forward and
>> not touch the boot time.
>
> Again, if you have been sitting in DDB, what exactly is the definition
> of "uptime" ?

This is clear.  The system is up while it is sitting in ddb.  It's actually
more active then average then, since doesn't idle or halt :-).

Bruce