Messages in this thread | | | Date | Mon, 30 Apr 2012 12:48:22 -0700 | From | John Stultz <> | Subject | Re: [PATCH 1/1] ntp: advertise correct TAI offset during leap second |
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On 04/27/2012 11:17 PM, Richard Cochran wrote: > On Fri, Apr 27, 2012 at 03:23:17PM -0700, John Stultz wrote: >> On 04/26/2012 05:11 AM, Richard Cochran wrote: >>> When repeating a UTC time value during a leap second (when the UTC >>> time should be 23:59:60), the TAI timescale should not stop. The kernel >>> NTP code increments the TAI offset one second too late. This patch fixes >>> the issue by incrementing the offset during the leap second itself. >>> >>> Signed-off-by: Richard Cochran<richardcochran@gmail.com> >> This looks good to me. Although, have you actually tested against an >> ntp client that sets the tai offset to make sure you're not >> duplicating any ADJ_TAI adjustment it might make? > No, I cooked up my own test program that uses the adjtimex interface > directly. I really am not very familiar with the ntp.org software. > > Wait a minute. If user space manages this variable, then shouldn't the > kernel leave it alone?
Right. That's why I'm asking. I actually haven't spent much time looking at how the tai value provided via adjtimex is handled, and I want to make sure its ok if we modify it from the kernel.
> This David Mills paper [1] gives a leap second example that does it > the "other" way from Linux (see Figure 4), repeating the new epoch > rather than the leap second. It may well be that ntp.org servers do > behave that way. However, the NIST file claims that this way is > unusual. > > So, you have a good question. But, if ntp.org uses the NIST second > method, shouldn't Linux do the same? > Not sure I'm following here. In Linux 23:59:60 is represented as 23:59:59 + TIME_OOP. Could you expand on what in particular is inconsistent here?
thanks -john
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