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From: David Newall on 10 Mar 2010 03:50
Dear Srinivas Nayak,

I don't suppose you're writing to a network mounted disk, with the
network device's clock about half a second behind your test machine?
Otherwise -- and I'm just guessing here, and will leave it to you to
UTSL -- this could be explained by use of two different algorithms for
converting a higher-resolution time source to the one-second
resolution. A truncation algorithm versus a rounding algorithm could
produce the result you demonstrate.

Regards,

David
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From: john stultz on 10 Mar 2010 12:20
On Tue, Mar 9, 2010 at 11:59 PM, Srinivas Nayak
<sinu_nayak2001(a)yahoo.co.in> wrote:
> I wrote a small program, that creates files at an interval of 1 minute. But the time at which the file is created and last written and the last modification time of the file as shown by ls command differs by 1 second. The code and the output is presented below. please let me know where could be the bug?
>
[snip]
> Some system info:
> ===========
> Linux new 2.6.24-19-server #1 SMP Wed Jun 18 14:44:47 UTC 2008 x86_64 GNU/Linux
> Gnu C � � � � � � � � �4.2.4
> Linux C Library � � � �2.7
> binutils � � � � � � � 2.18.0.20080103
> util-linux � � � � � � 2.13.1
> Console-tools � � � � �0.2.3
> Sh-utils � � � � � � � 6.10
> ===========

Hrm. Is CONFIG_NO_HZ enabled? If so this is a known issue. The
filesystem timestamps use xtime, which is normally updated every HZ.
However to reduce overhead with NO_HZ we changed the update to be a
half-second, which can cause issues like what you describe.

The issue has since been resolved, so I'd be interested to hear if you
can still reproduce it on a more recent kernel.

thanks
-john
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