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

[Poul-Henning Kamp]

In message <435921F1.5E9050AD at networx.ch>, Andre Oppermann writes:
>> >IMO it's this:
>> >
>> > Uptime is the time the operating was available to present it's common
>> > services to userland.  That excludes any suspend and ddb times.  Single
>> > user mode however counts because the OS was servicing userland even if
>> > there was only one user.  Uptime is represented in SI seconds.
>> 
>> I can live with this definition.
>> 
>> So now we just need to be able to reliably measure the "not-uptime".
>
>Umm...  Whenever the onesec tick is not incrementing the uptime (and
>monotonic) counter.  Which conviniently already is the case when OS is
>suspended or in DDB.

Uhm, yes.  Only...

How do we measure the time our clock does _not_ tick ?

We need to use another clock for that.

The RTC comes to mind, but it's precision leaves a lot to be
desired.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.