Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 18 Jul 2007 23:31:13 +0200 | From | "Alessandro Suardi" <> | Subject | Re: clocksource change of behavior in 2.6.22 compared to 2.6.20 causes massive system clock slowdown |
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On 7/18/07, john stultz <johnstul@us.ibm.com> wrote: > On Wed, 2007-07-18 at 00:31 +0200, Alessandro Suardi wrote: > > On 7/11/07, john stultz <johnstul@us.ibm.com> wrote: > > > On Wed, 2007-07-11 at 01:31 +0200, Alessandro Suardi wrote: > > > > On 7/10/07, john stultz <johnstul@us.ibm.com> wrote: > > > > > On Tue, 2007-07-10 at 00:29 -0700, Andrew Morton wrote: > > > > > > On Mon, 9 Jul 2007 16:27:59 +0200 "Alessandro Suardi" <alessandro.suardi@gmail.com> wrote: > > > > > > > > > > > > > My oldish AMD K7-800's clock began falling behind after > > > > > > > rebooting from 2.6.20 (and 109 days uptime with a spotless > > > > > > > clock) into 2.6.22; time lost is about four minutes each hour. > > > > > > > > > > > > > > Turns out that 2.6.22 marks my TSC as unstable and starts > > > > > > > using PIT instead. Rebooting 2.6.22 with clocksource=tsc > > > > > > > gets the original stable system time back. > > > > > > > > > > Alessandro, > > > > > Can you send me dmesg output for 2.6.20 and 2.6.22 (without > > > > > clocksource=tsc)? > > > > > > > > Actually, I lied a little bit - it was 2.6.22 with clock=tsc (which > > > > warns on boot about clock= being deprecated in favor of > > > > clocksource= ). I assume behavior is identical for now. > > > > > > > > Please find attached the dmesg ring (incomplete, as the > > > > kernel ring size I have seems too small to hold the full > > > > buffer, but it seems to have all the interesting stuff) of > > > > 2.6.20, 2.6.22, 2.6.22 with clock=tsc. > > > > > > > > If you need more info, just ask. I'll be out of the country > > > > from July 12 to the morning of July 16, and again from > > > > July 17 to July 20, so if you'd rather get at this later on, > > > > it's okay for me ;) > > > > > > You're dmesg output got chopped at the top. Please increase the kernel > > > log buffer size. > > > > Done, please find attached both 2620 and 2622 full dmesg output, > > with no clock= or clocksource= parameters. > > > > > Sounds like your PIT frequency is out of whack, and I'm guessing the > > > generic clocksource watchdog blames the TSC and disqualifies it. > > > > > > Few things to check: > > > 1) Make sure you're running the latest BIOS. > > > > I'm probably not, though I'm not sure I'd flash anything on such > > an old machine - been running it since RedHat 9 with the > > current BIOS. Plus, I removed the floppy drive to make room > > for an extra IDE disk... it'd take me a little bit to find out whether > > I still have the floppy drive around. > > > > > 2) See if booting w/ noapic changes anything > > > > Nope, 2622+noapic => PIT is still used and clock very quickly > > lags behind. > > > > For the moment being I'll keep booting with clocksource=tsc. > > Let me know whether you want me to test anything more... > > Hmm. One other thing to check: If you boot 2.6.20 w/ clocksource=pit, is > it consistent w/ 2.6.22 and same slow timekeeping issue shows up?
Yes, 2620+clocksource=pit is noticeably slow in timekeeping as well.
From my laptop (Dell D610 running 2.6.22-git10 on top of Fedora7) I ssh'd into my K7-800 and with two terminal windows I ran the same simple bash loop, starting more or less at the same time: while :; do let i=i+1; echo $i; sleep 1; done
When the laptop reached 60, the K7-800 was at 57. In order to eliminate any possible doubt about how I started the two sessions, I let the loop run; when the laptop reached 120, the K7-800 was displaying 114. So it's indeed a 3-second per minute loss with PIT in either 2620 or 2622.
--alessandro
"Did you get married but forgot to get divorced ?"
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