> Followup to: <Pine.LNX.3.95.981230105754.6194F-100000@penguin.transmeta.com>
> By author: Linus Torvalds <torvalds@transmeta.com>
> In newsgroup: linux.dev.kernel
> >
> > The "rdtsc" thing _is_ needed even for UP systems.
> >
> > Look at the code generated for do_gettimeofday() some time - it's a
> > worthwhile optimization to do statically.
> >
> > (And if you wonder why I care about gettimeofday(), just look at the
> > system call distribution for a lot of programs, including most X
> > programs).
> >
> > As I mentioned in my email, it may be a valid thing to expand the choices
> > a bit (ie add a choice between i486 and i586), but the static "rdtsc"
> > thing definitely stays.
> >
>
> Not only that, but it is friggin' vital for a time server.
>
> -hpa
> --
A lot of machines don't have very accurate bus-clock crystals and
many are now using #%$@*&$ PZST piezoelectric resonators because
they are cheap. Here is a log of once-a-day setting of my time-server
against NIST. This is a dual pentium 400MHz 'Thunder' board.
Reference time = Thu Dec 10 00:00:07 1998
My time = Thu Dec 10 00:00:01 1998
Difference = -6 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Fri Dec 11 00:00:04 1998
My time = Fri Dec 11 00:00:01 1998
Difference = -3 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Sun Dec 13 00:00:29 1998
My time = Sun Dec 13 00:00:00 1998
Difference = -29 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Tue Dec 15 00:00:10 1998
My time = Tue Dec 15 00:00:00 1998
Difference = -10 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Wed Dec 16 00:00:14 1998
My time = Wed Dec 16 00:00:00 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Fri Dec 18 00:00:28 1998
My time = Fri Dec 18 00:00:00 1998
Difference = -28 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Sat Dec 19 00:00:14 1998
My time = Sat Dec 19 00:00:00 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Sun Dec 20 00:00:14 1998
My time = Sun Dec 20 00:00:00 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Mon Dec 21 00:00:15 1998
My time = Mon Dec 21 00:00:00 1998
Difference = -15 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Tue Dec 22 00:00:14 1998
My time = Tue Dec 22 00:00:00 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Wed Dec 23 00:00:14 1998
My time = Wed Dec 23 00:00:00 1998
Difference = -14 seconds
Reference time = Thu Dec 24 00:00:06 1998
My time = Thu Dec 24 00:00:00 1998
Difference = -6 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Fri Dec 25 00:00:15 1998
My time = Fri Dec 25 00:00:01 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Sat Dec 26 00:00:14 1998
My time = Sat Dec 26 00:00:00 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Sun Dec 27 00:00:21 1998
My time = Sun Dec 27 00:00:06 1998
Difference = -15 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Mon Dec 28 00:00:14 1998
My time = Mon Dec 28 00:00:00 1998
Difference = -14 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Tue Dec 29 00:00:15 1998
My time = Tue Dec 29 00:00:01 1998
Difference = -14 seconds
Setting hardware clock to Tue Dec 29 13:04:45 EST 1998
Reference time = Wed Dec 30 00:00:07 1998
My time = Wed Dec 30 00:00:00 1998
Difference = -7 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
Reference time = Thu Dec 31 00:00:15 1998
My time = Thu Dec 31 00:00:00 1998
Difference = -15 seconds
Time set by time-A.timefreq.bldrdoc.gov (132.163.135.130)
As you can see, it typically loses 15 seconds per day. Since the
time is reset every day at around midnight, it's not too bad.
Cheers,
Dick Johnson
***** FILE SYSTEM WAS MODIFIED *****
Penguin : Linux version 2.1.131 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.
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