Re: /proc or ps tools bug? 2.6.3, time is off

[David Ford]

Albert Cahalan wrote:

> On Tue, 2004-02-24 at 20:58, David Ford wrote:
>  
>
> > Kernel 2.6.3, procps 3.2.0
> >
> > # while [ 1 ]; do (ps aux|grep "grep ps aux" && date) ; sleep 1; done
> > root     20043  0.0  0.0  1504  456 pts/0    R    20:45   0:00 grep grep ps aux
> > Tue Feb 24 20:45:25 EST 2004
> > root     20062  0.0  0.0  1504  460 pts/0    S    20:45   0:00 grep grep ps aux
> > Tue Feb 24 20:45:26 EST 2004
> > root     20081  0.0  0.0  1504  460 pts/0    S    20:46   0:00 grep grep ps aux
> > Tue Feb 24 20:45:27 EST 2004
> >
> > Note the change in the timestamp as reported by 'ps' v.s. the time 
> > reported by 'date'.
> >
> > Repeatable every time at 26 seconds after the minute +/- a portion of a 
> > second.
> >    
>
> I'm not seeing it, with:
>
> procps    both 3.1.8 and procps 3.2.0+
> kernel    2.6.0-test11
> library   glibc 2.3
> hardware  uniprocessor G4 Mac
> ntp       none (and you can tell by my email!)
>
> Run "ps --info" to gather much of this data.
>
> Note that time is a very awkward thing. You boot up,
> with some incorrect clock. Then you adjust the time.
> Later, you may discover that your clock has been
> running too slow. So you adjust the frequency, but
> what about the time that has already passed? Should
> you change the boot time to represent what is now
> known about your clock? What if, by doing so, you
> cause some processes to have started before boot?
> Then again, perhaps due to temperature change, you
> discover that your clock frequency is wrong... This
> is without even getting into the concept of leap
> seconds, which are determined a few months in advance.
>
> Two guesses:
>
> 1. leap seconds
> 2. SMP, with cycle counters out of sync
>  

I'm seeing it on two machines now, I'm going to test on more machines as 
I get access.  The second machine is my notebook with procps 3.1.15 on 
it, and it does it at the 46 second mark, also 2.6.3.

I can see if a process long in the past would have a different time set 
on it, but shouldn't the entry in /proc coincide with the system clock 
that date is accessing?  Or how many different "clocks" does the kernel 
have going?

powerix conf.d # ps --info
BSD j    OL_j
BSD l    OL_l
BSD s    OL_s
BSD u    OL_u
BSD v    OL_v
SysV -f  (none)
SysV -fl (none)
SysV -j  (none)
SysV -l  (none)

procps version 3.1.15
Linux version 2.6.3
Compiled with: glibc 2.3, gcc 3.3

header_gap=-1 lines_to_next_header=1
screen_cols=91 screen_rows=29

personality=0x00000000 (from "unknown")
EUID=0 TTY=136,3 Hertz=100 PAGE_SIZE=4096 page_size=4096
sizeof(proc_t)=492 sizeof(long)=4 sizeof(KLONG)=4
archdefs: i386
namelist_file="<no System.map file>"

Actually, it seems that there is a -significant- time difference in this 
phantom clock now, I suspended my notebook to bring it home from the 
station, and now this time difference is greater than 9 minutes.  I 
suspect it's roughly 46 seconds plus the amount of time that my notebook 
was suspended.  Yes, I'm running ntpd.

root     16894  0.0  0.0  1544  484 pts/3    S    Feb24   0:00 grep grep ps
Wed Feb 25 00:09:09 EST 2004

David

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