linux-kernel - Re: Apparent backward time travel in timestamps on file creation

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Message-ID: <CALAqxLWR0g1dEOO0kMtpDL9grmKxTVx7ELhsW6055saQi+F1HA@mail.gmail.com>
Date:   Thu, 30 Mar 2017 13:03:50 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: Apparent backward time travel in timestamps on file creation

On Thu, Mar 30, 2017 at 12:35 PM, David Howells <dhowells@...hat.com> wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> The difference can be quite noticeable - basically the
>> "gettimeofday()" time will interpolate within timer ticks, while
>> "xtime" is just the truncated "time at timer tick" value _without_ the
>> correction.
>
> Is there any way to determine the error bar, do you know?  Or do I just make
> up a fudge factor?

Again, I'd utilize clock_gettime(CLOCK_REALTIME_COARSE, ...) for this
instead of playing with fudge factors.

thanks
-john