Andi Kleen writes: > Just to avoid spreading misinformation: modulo some new broken hardware > (which we always try to work around when found) i386/x86-64 gettimeofday > is monotonic. AFAIK on the currently known hardware it should be generally > ok. > > However ntpd can always screw you up, but that's inherent in the design.
On powerpc we manage to keep gettimeofday monotonic even when ntpd is adjusting the clock. We have 3 parameters used to convert a value from the timebase register to the time of day, and these parameters are adjusted if necessary at the beginning of each tick, based on the value returned by current_tick_length(). The point is that current_tick_length() tells you at the *beginning* of each tick how much time will be added on to xtime at the *end* of that tick, and that makes it possible to aim the interpolation to hit the same value as xtime at the end of each tick. Clearly if you make a discrete jump backwards with settimeofday or adjtime, it's impossible to keep gettimeofday monotonic, but apart from that it's monotonic on powerpc. At least, that's the way it's supposed to work. I hope the recent timekeeping changes haven't broken it. :) Paul. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
