Re: 2.6.16-rc2 powerpc timestamp skew

[Roger Leigh]

Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> writes:

> On Sun, 2006-02-12 at 17:13 +0000, Roger Leigh wrote:
>> Hi folks,
>> 
>> When running a 2.6.16-rc2 kernel on a powerpc system (Mac Mini;
>> Freescale 7447A):
>> 
>> $ date && touch f && ls -l f && rm -f f && date
>> Sun Feb 12 12:20:14 GMT 2006
>> -rw-r--r-- 1 rleigh rleigh 0 2006-02-12 12:23
>> Sun Feb 12 12:20:14 GMT 2006
>> 
>> Notice the timestamp is 3 minutes in the future compared with the
>> system time.  "make" is not a very happy bunny running on this kernel
>> due to every touched file being 3 minutes in the future.
>> 
>> When the same command is run on 2.6.15.3:
>> 
>> $ date && touch f && ls -l f && rm -f f && date
>> Sun Feb 12 14:27:27 GMT 2006
>> -rw-r--r-- 1 rleigh rleigh 0 2006-02-12 14:27
>> Sun Feb 12 14:27:27 GMT 2006
>> 
>> In this case the times are identical, as you would expect.
>> 
>> In both these cases, the chrony NTP daemon is running, if that might
>> be a problem.
>
> Can you strace vs. ltrace and see if the gettimeofday or clock_gettime
> syscalls are ever called ?

           | strace        | ltrace
-----------+---------------+------------------------------------
2.6.15     |               |
date       | clock_gettime | clock_gettime -> SYS_clock_gettime,
           |               |   localtime, strftime
touch      | utimes        | futimes -> SYS_utimes
           |               |
2.6.16-rc2 |               |
date       | clock_gettime | clock_gettime -> SYS_clock_gettime,
           |               |   localtime, strftime
touch      | utimes        | futimes -> SYS_utimes

[clock_gettime(CLOCK_REALTIME, {1139826613, 157402000}) = 0]

> I wonder if you have a glibc new enough to
> use the vDSO to obtain the time or if it's using the syscall... The vDSO
> on ppc32 is very new.

It's glibc 2.3.5 (Debian libc6 2.3.5-13).

> Also, are your kernels built with ARCH=ppc or ARCH=powerpc ?

ppc.


Thanks,
Roger

-- 
Roger Leigh
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