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Re: kern/45626: System time does not advance correctly when noatime is specified for /var
The following reply was made to PR kern/45626; it has been noted by GNATS.
From: Donald Allen <donaldcallen%gmail.com@localhost>
To: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
Cc: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost,
Subject: Re: kern/45626: System time does not advance correctly when noatime
is specified for /var
Date: Fri, 18 Nov 2011 13:47:41 -0500
On Fri, Nov 18, 2011 at 10:06 AM, Donald Allen
> On Fri, Nov 18, 2011 at 9:33 AM, Manuel Bouyer
> <bouyer%antioche.eu.org@localhost> w=
>> On Fri, Nov 18, 2011 at 01:25:03PM +0000, Donald Allen wrote:
>> > =A0[...]
>> > =A0sysctl -a | grep kern.timecounter
>> > =A0which I did:
>> > =A0kern.timecounter.choice =3D TSC(q=3D3000, f=3D67750617510 Hz) clock=
>> > =A0f=3D100 Hz) ichlpcib0(q=3D1000, f=3D3579545 Hz) hpet0(q=3D2000, f=
>> > =A0ACPI-Fast(q=3D1000, f=3D3579545 Hz) lapic(q=3D-100, f=3D266097187 H=
>> > =A0f=3D1193182 Hz) dummy(q=3D-1000000, f=3D1000000 Hz)
>> > =A0kern.timecounter.hardware =3D TSC
>> > =A0kern.timecounter.timestepwarnings =3D 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
> [ =A0 =A00.000000] Fast TSC calibration failed
> [ =A0 =A00.000000] TSC: PIT calibration matches HPET. 1 loops
> [ =A0 =A01.336163] 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.
>> > =A0He also suggested trying
>> > =A0sysctl -w kern.timecounter.hardware=3Dhpet0
>> > =A0>
>> > =A0> and see if that fixes it.
>> > =A0>
>> > =A0It does:
>> > [...]
>> > =A0However, after doing this, the system behaved in odd ways. I had tr=
>> > =A0shutting X down, the system seemed not to be hearing the (USB) keyb=
>> > =A0couldn't log in after doing ctrl-alt-f2). I finally got it shut dow=
>> > =A0rebooted, ending this experiment.
>> > =A0I then decided to try a newer kernel, and installed the kernel from=
>> > =A011/17 snapshot. Upon booting the system this morning (with all the =
>> > =A0systems, including /var, mounted async,noatime), I quickly observed=
>> > =A0clock 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.
The system has been up almost four hours and time-keeping is working
fine, so your suggestion to switch to another source of ticks has
fixed my problem.
I'd also like to mention that I've had this machine for a few years
now, and, in addition to Linux, I have tried OpenBSD and FreeBSD on it
(both of which were abandoned for good reasons, which I won't go into
here). I had no problems with time-keeping with them, either. So
you've got a couple of BSD references, in addition to Linux, for ideas
on working around the TSC issue.
Again, thanks very much for your help.
> Thanks for your help.
>> You can also try other available timecounters (try ichlpcib0 or i8254
>> for exampe).
>> Manuel Bouyer <bouyer%antioche.eu.org@localhost>
>> =A0 =A0 NetBSD: 26 ans d'experience feront toujours la difference
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