Messages in this thread | | | Date | Tue, 23 Aug 2005 17:29:54 -0700 | From | George Anzinger <> | Subject | Re: [RFC - 0/9] Generic timekeeping subsystem (v. B5) |
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Roman Zippel wrote: > Hi, > > On Tue, 23 Aug 2005, john stultz wrote: > > >>I'm assuming gettimeofday()/clock_gettime() looks something like: >> xtime + (get_cycles()-last_update)*(mult+ntp_adj)>>shift > > > Where did you get the ntp_adj from? It's not in my example. > gettimeofday() was in the previous mail: "xtime + (cycle_offset * mult + > error) >> shift". The difference between system time and reference > time is really important. gettimeofday() returns the system time, NTP > controls the reference time and these two are synchronized regularly. > I didn't see that anywhere in your example. > John, If I read your example right, the problem is when the NTP adjustment changes while the two clocks are out of sync (because of a late tick). It would appear that gettimeofday would need to know that the NTP adjustment is changing (and to what). It would also appear that this is known by the ntp code and could be made available to gettimeofday. If it is changing due to an NTP call, that system call, itself, should/must force synchronization. So the only case gettimeofday needs to worry/know about is that an adjustment is to change at time X to value Y. Also, me thinks there is only one such change that can be present at any given time.
Hope this helps... -- George Anzinger george@mvista.com HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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