linux-kernel - Re: BUG: Is it a bug in Linux time() function or Linux OS calls?

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Message-ID: <1f1b08da1003100919k57d8cc6au6ff753ebf5b6c2f8@mail.gmail.com>
Date:	Wed, 10 Mar 2010 09:19:30 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Srinivas Nayak <sinu_nayak2001@...oo.co.in>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG: Is it a bug in Linux time() function or Linux OS calls?

On Tue, Mar 9, 2010 at 11:59 PM, Srinivas Nayak
<sinu_nayak2001@...oo.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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