Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH] correct inconsistent ntp interval/tick_length usage | From | john stultz <> | Date | Wed, 30 Jan 2008 18:16:16 -0800 |
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On Thu, 2008-01-31 at 02:55 +0100, Roman Zippel wrote: > Hi, > > On Tue, 29 Jan 2008, john stultz wrote: > > > +/* Because using NSEC_PER_SEC would be too easy */ > > +#define NTP_INTERVAL_LENGTH ((((s64)TICK_USEC*NSEC_PER_USEC*USER_HZ)+CLOCK_TICK_ADJUST)/NTP_INTERVAL_FREQ) > > Why are you using USER_HZ? Did you test this with HZ!=100?
I'm using USER_HZ, because ntp_update_frequency() uses USER_HZ.
And my tests were run at HZ=1000.
> Anyway, please don't make more complicated than it already is. > What I said previously about the update interval is still valid, so the > correct solution is to use the simpler NTP_INTERVAL_LENGTH calculation > from my last mail and to omit the correction for NO_HZ.
I'm not sure I follow how having two separate and totally different definitions of NTP_INTERVAL_LENGTH is less complicated then my last patch.
Maybe I'm missing something from your suggestion? Or maybe could you contribute your suggestion as a patch?
My concern is we state the accumulation interval is X ns long. Then current_tick_length() is to return (X + ntp_adjustment), so each accumulation interval we can keep track of the error and adjust our interval length.
So if ntp_update_frequency() sets tick_length_base to be:
u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << TICK_LENGTH_SHIFT; second_length += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT; second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
tick_length_base = second_length; do_div(tick_length_base, NTP_INTERVAL_FREQ);
The above is basically (X + part of ntp_adjustment)
So I'm trying to calculate the X as:
#define NTP_INTERVAL_LENGTH ((((s64)TICK_USEC*NSEC_PER_USEC*USER_HZ)+CLOCK_TICK_ADJUST)/NTP_INTERVAL_FREQ)
thanks -john
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