lkml.org 
[lkml]   [2004]   [Aug]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] Re: boot time, process start time, and NOW time
    Tim Schmielau wrote:
    > On Mon, 16 Aug 2004, Andrew Morton wrote:
    >
    >
    >>OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:
    >>
    >>>Albert Cahalan <albert@users.sf.net> writes:
    >>>
    >>>
    >>>>Even with the 2.6.7 kernel, I'm still getting reports of process
    >>>>start times wandering. Here is an example:
    >>>>
    >>>> "About 12 hours since reboot to 2.6.7 there was already a
    >>>> difference of about 7 seconds between the real start time
    >>>> and the start time reported by ps. Now, 24 hours since reboot
    >>>> the difference is 10 seconds."
    >>>>
    >>>>The calculation used is:
    >>>>
    >>>> now - uptime + time_from_boot_to_process_start
    >>>
    >>>Start-time and uptime is using different source. Looks like the
    >>>jiffies was added bogus lost counts.
    >>>
    >>>quick hack. Does this change the behavior?
    >>
    >>Where did this all end up? Complaints about wandering start times are
    >>persistent, and it'd be nice to get some fix in place...
    >>
    >>Thanks.
    >>
    >
    >
    > Seems my analysis of the problem wasn't perceived as such.
    >
    > The problem is that in the above calculation
    >
    > now - uptime + time_from_boot_to_process_start
    >
    > "uptime" currently is an ntp-corrected precise time, while
    > "time_from_boot_to_process_start" just is the free-running "jiffies"
    > value.

    I see you think you have the solution, but I guess I am just dense here. May be
    you could help me to see the error of my ways. Here is my thinking:

    "now" is from gettimeofday() and as such is ntp corrected.
    "uptime" is also corrected. In fact it is "now" + "wall_to_monotonic". And
    "wall_to_monotonic" is _only_ changed by do_settime() when the clock is set.
    "time_from_boot_to_process_start" is the same as "start_time" restated in
    seconds, i.e. it is a constant. So, either one or more of the above assumtions
    is wrong, or somebody is twiddling the clock. Otherwise I don't see how the
    start time can move at all.
    >
    > The problem is easily reproducible for me. It goes away if the change
    > that rebased /proc/uptime on posix monotonic time and my followup patch to
    > fix the resulting rounding issues in jiffies64_to_clock_t() are backed out
    > with the following patch.
    >

    --
    George Anzinger george@mvista.com
    High-res-timers: http://sourceforge.net/projects/high-res-timers/
    Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 14:05    [W:3.801 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site