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Re: kern/45626: System time does not advance correctly when noatime is specified for /var
On Fri, Nov 18, 2011 at 9:33 AM, Manuel Bouyer
> On Fri, Nov 18, 2011 at 01:25:03PM +0000, Donald Allen wrote:
> > [...]
> > sysctl -a | grep kern.timecounter
> > which I did:
> > kern.timecounter.choice = TSC(q=3000, f=67750617510 Hz) clockinterrupt(q=0,
> > f=100 Hz) ichlpcib0(q=1000, f=3579545 Hz) hpet0(q=2000, f=14318179 Hz)
> > ACPI-Fast(q=1000, f=3579545 Hz) lapic(q=-100, f=266097187 Hz) i8254(q=100,
> > f=1193182 Hz) dummy(q=-1000000, f=1000000 Hz)
> > kern.timecounter.hardware = TSC
> > kern.timecounter.timestepwarnings = 0
> TSC is clearly wrong here, I'm sure you don't have a 67Ghz CPU :)
That's certainly true.
I've got NetBSD installed next to Slackware Linux on this machine,
running the 3.0.8 kernel from kernel.org. I've had no problem with
time-keeping in Linux on the machine, so out of curiosity, I brought
Linux up and had a look at the dmesg:
dca@salome:~$ sudo dmesg | fgrep TSC
[ 0.000000] Fast TSC calibration failed
[ 0.000000] TSC: PIT calibration matches HPET. 1 loops
[ 1.336163] Refined TSC clocksource calibration: 2393.976 MHz.
I could be wrong, but that suggests to me that the Linux kernel
noticed the TSC oddness and somehow compensated. Perhaps a look at
what they're doing is in order.
> > He also suggested trying
> > sysctl -w kern.timecounter.hardware=hpet0
> > >
> > > and see if that fixes it.
> > >
> > It does:
> > [...]
> > However, after doing this, the system behaved in odd ways. I had trouble
> > shutting X down, the system seemed not to be hearing the (USB) keyboard (I
> > couldn't log in after doing ctrl-alt-f2). I finally got it shut down and
> > rebooted, ending this experiment.
> > I then decided to try a newer kernel, and installed the kernel from the
> > 11/17 snapshot. Upon booting the system this morning (with all the file
> > systems, including /var, mounted async,noatime), I quickly observed the
> > clock problem.
> You should try setting
> in /etc/sysctl.conf, so that the change is applied at boot.
> The odd behavior you see may be caused by processes started before
> the timecounter change.
That makes sense.
I've made the change you suggested to /etc/sysctl.conf and brought the
system back up. I will use it for my work today and keep an eye on the
time-keeping. So far it's working fine.
Thanks for your help.
> You can also try other available timecounters (try ichlpcib0 or i8254
> for exampe).
> Manuel Bouyer <bouyer%antioche.eu.org@localhost>
> NetBSD: 26 ans d'experience feront toujours la difference
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