Benjamin Gamsa wrote:
Paul Mackerras wrote:
Ben Gamsa writes:
It appears to be the case that when the time on the system is around
the epoch (1970), that time will occasionally jump forward and then
backward by about 17592 seconds. When it jumps forward, it always
jumps back a few milliseconds later. However, it's not always easy
to catch these occurrences. The delta is more specifically about
17592186059 usec, give or take a few 10s of microseconds (most of the
time), despite the fact that the user-level program I have that is
testing it only checks every 10 milliseconds.
I don't think the time code in the kernel is designed to handle
negative values, i.e., times before the epoch. If you want it to do
that you'll have to check places like arch/powerpc/kernel/time.c,
kernel/time/timekeeping.c, arch/powerpc/include/asm/time.h, etc., and
make sure that it uses signed types where necessary and that the
arithmetic is correct.
The time never goes negative. It starts off at the epoch and moves
forward, but sometimes it jumps forward by 17952 seconds, and then
immediately jumps back. But it never goes negative (or prior to 1970).
One important thing I forgot to add is that ntpd is running on this
system, but the ntp servers are not available. I suspect the problem
may be related to ntpd, even though I've seen the time jump even when I
had ntpd stopped within gdb. I've not yet been able to confirm if the
problem still occurs when ntpd is never even started, although I will be
testing that soon (the tests often require many hours to establish if
there are no jumps).
ben
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