RE: Corrected gettimeofday() test code

From: Kris Kennaway [mailto:kris_at_obsecurity.org]
> 
> I forwarded the reports of timecounter problems to phk, and he asked
> that people who are seeing timecounter problems provide FULL details
> of their system configuration, including:
> 
> * dmesg
> 
> * kernel configuration
> 
> * compiler options
> 
> * time-related system configuration (whether ntpd/timed/ntpdate is
> running, and if so whether it's correcting for a seriously drifting
> clock)
> 
> * The kernel timecounter configuration, e.g. the
> kern.timecounter.method and kern.timecounter.hardware sysctls, and
> whether changing them has any effect.
> 
> * The exact output of the corrected test program below (the original
> would give spurious errors if it didn't run at least once a second,
> which may have been confusing some people if their systems were
> sufficiently loaded).
> 
> * The system status when the problem is observed (i.e. does it only
> occur under load; what else is running at the time)
> 

For this config (below), kern.timecounter.method=0 reproduces the
problem, kern.timecounter.method=1 does not.

Output in 'error' case:
1070147643.248866 1070147651.028646 1070147643.248866 1070147651.028646
1070147656.287818 1070147664.067692 1070147656.287818 1070147664.067692
1070147659.326429 1070147667.106238 1070147659.326429 1070147667.106238
1070147668.370071 1070147676.149884 1070147668.370071 1070147676.149884
1070147681.433111 1070147689.212926 1070147681.433111 1070147689.212926
1070147683.418743 1070147691.198632 1070147683.418743 1070147691.198632

problem shows up within ~30s of starting the test program, and the messages
will come out about once per 1-5s period after that, not regularly.

kern.timecounter.hardware: TSC

on this machine, i have others which are i8254 which do it too.

hw.ncpu=1

compiler flags:
COPTFLAGS= -O2 -pipe -malign-loops=4 -malign-jumps=4 -malign-functions=4
-mcpu=i686 -march=i686 -fno-gcse -g



machine is running 4.7-RELEASE-p2.

dmesg, kernel config attached.


Intel-specific functions:
Version 00000673:
Type 0 - Original OEM
Family 6 - Pentium Pro
Model 7 - Pentium III/Pentium III Xeon - external L2 cache
Stepping 3
Reserved 0

from cpuid.

ntpd -p /var/run/ntpd.pid -b -g -A
runs.

Clock does not drift much, less than 2s/day. Clock is 
stepped when system boots. There is a chimer on our router 
which broadcasts ntp time every minute. ntpd is not
observed to step clock.

On the 8254 machine [a dual 0f27 xeon, 533 FSB with HTT enabled]
1070147645.119531 1070148340.497729 1070148339.-693880469 1070148340.497729

both systems were unloaded. This was with the corrected program
you included.

--don