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Old 02-26-2009, 12:47 AM
Yaroslav Halchenko
 
Default dmesg timestamps vs uptime

My today reported (and reassigned to linux2.6) bug #517122
doesn't gimme rest. One of the problem of analysis of traces is that
some times are recorded since epoch, some are the kernel's "uptime".
what puzzles me is:

* Difference between dmesg timestamp and /proc/uptime

$> tcpdump -i bond0 -tt -vvv -n "(dst host raider or src host raider)" -s 192 | head -3; dmesg | tail -1; echo "/proc/uptime"; cat /proc/uptime
...
[250851.259481] device eth1 left promiscuous mode
/proc/uptime
241764.70 224706.33

so I have timestamp in kernel messages bigger than uptime

I wonder why is that? different clock source? any other drift?

or may be 'kernel time' in dmesg is some kind of tick, not time per se?

* Is there an easy way to convert (reliably ) timestamp in dmesg to
time since epoch (with mksec precision of cause), so I could easily compare
with output in strace and alike.

Thanks in advance!!!!
--
Yaroslav Halchenko
Research Assistant, Psychology Department, Rutgers-Newark
Student Ph.D. @ CS Dept. NJIT
Office: (973) 353-1412 | FWD: 82823 | Fax: (973) 353-1171
101 Warren Str, Smith Hall, Rm 4-105, Newark NJ 07102
WWW: http://www.linkedin.com/in/yarik
 
Old 02-26-2009, 01:07 AM
Yaroslav Halchenko
 
Default dmesg timestamps vs uptime

I guess kernel/sched_clock.c gave me the answer to the 1st question...
even answered why I saw some timestamps jumping backwards while I was
monitoring debug msgs of RPC + NFS , I guess they came from different
CPUs

now I wonder if there is a tool which would "work" along some other
process and monitor those 'semi stable' clocks so later on provide more
or less reliable and consistent conversion into time since epoch.

On Wed, 25 Feb 2009, Yaroslav Halchenko wrote:
> * Difference between dmesg timestamp and /proc/uptime

> * Is there an easy way to convert (reliably ) timestamp in dmesg to
> time since epoch (with mksec precision of cause), so I could easily compare
> with output in strace and alike.

> Thanks in advance!!!!
--
Yaroslav Halchenko
Ph.D. Student CS Dept. NJIT


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