Re: cvs commit: src/sys/kern

[Paul Herman <pherman@xxxxxxxxxxxxxxx>]

On Sat, 4 Dec 2004, Matthew Dillon wrote:

>  Log:
>  Fix the boottime calculation when the time of day is set in absolute terms.
>  We want boottime to be calculated based on the current real time minus our
>  best uptime guess.  gd_time_seconds survives a lot of time issues and is our
>  best uptime guess and since it is already used to calculate the new basetime,
>  we can just assign boottime to basetime.

On an additional note -- and I suppose anything at this point is 
nitpicking -- would it be worthwhile to preserve the original 
drift?  Take an extreme example with the current code with a 
machine booted at 12:00:00 when the clock adds a second every 30 
seconds compared to a reference clock:

        basetime = 11:59:58
        boottime = 12:00:00
  reference time = 12:01:00
 gd_time_seconds = 62
    nanouptime() = 00:01:02
wallclock uptime = 00:01:00
     w(1) uptime = 00:01:00

Now, reset time on the reference clock (and machine) forward 1 
minute to 12:02:00

        basetime = 12:00:58
        boottime = 12:00:58
  reference time = 12:02:00
 gd_time_seconds = 62
    nanouptime() = 00:01:02
wallclock uptime = 00:01:00
     w(1) uptime = 00:01:02

So (if I got the logic all right) the w(1) uptime reported would be 
wrong.  If we could add the original 2 second difference between 
boottime & basetime back to boottime, I think things should be 
better.

Thoughts?  Am I getting too anal?  :-)
-Paul.

void
set_timeofday(struct timespec *ts)
{
        struct timespec ts2, drift;

        /*
         * XXX SMP / non-atomic basetime updates
         */
        crit_enter();
	drift.tv_sec = boottime.tv_sec - basetime.tv_sec;
	drift.tv_nsec = boottime.tv_nsec - basetime.tv_nsec;
        nanouptime(&ts2);
        basetime.tv_sec = ts->tv_sec - ts2.tv_sec;
        basetime.tv_nsec = ts->tv_nsec - ts2.tv_nsec;
        if (basetime.tv_nsec < 0) {
            basetime.tv_nsec += 1000000000;
            --basetime.tv_sec;
        }
        boottime.tv_sec = basetime.tv_sec + drift.tv_sec;
        boottime.tv_nsec = basetime.tv_nsec + drift.tv_nsec;
        timedelta = 0;
        crit_exit();
}