2011/9/27 Miguel Gonçalves <[email protected]>: > 2011/9/27 Dave Hart <[email protected]> >> >> I think you're simply confused. The FreeBSD sysctl you modified isn't >> adjusting the TSC frequency. It's adjusting FreeBSD's estimate of the >> TSC frequency. I stand by my understanding that a positive frequency >> compensation reported by ntpd means the clock's uncompensated rate is >> slow. > > Dear Dave, > > As you hold an ntp.org mail account I will trust you. But, why did the > frequency adjustment in loopstats reduced drastically when I changed the > sysctl variable? I assumed NTP did not see the sysctl variable.
I don't suggest you take my word for it, but reason it yourself. Your system clock is implemented on top of the TSC. Your earlier emails seemed to indicate you believed your sysctl adjustment was resulting in your TSC rate being changed to match, however, the knob you turned instead adjusted the system's estimate of how many beats of TSC equate to 1 SI second, while the TSC's actual rate is unchanged. Decreasing the TSC frequency estimate sysctl means FreeBSD will run its UTC clock faster, as fewer TSC beats are required from the fixed-rate TSC for each SI second advanced. As I would expect, speeding up a system clock which is running slower than UTC to close to UTC's rate meant ntpd needed a less-positive frequency compensation (drift). > Anyway, can I let the variable stay as is and let NTP do the adjustment? Yes. Cheers, Dave Hart _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
