NTP broken?
NTP on Linux 2.4.17/IA64 appears broken. ntpd never seems to be able
to pull the PLL into sync, even after using ntpdate to set the clock to the correct server time.
What are other peoples' experiences with NTP on IA64?
Peter C
Peter Chubb <[email protected]> writes:
|> NTP on Linux 2.4.17/IA64 appears broken. ntpd never seems to be able |> to pull the PLL into sync, even after using ntpdate to set the clock |> to the correct server time. |> |> What are other peoples' experiences with NTP on IA64?
It appears to be working correctly on all our machines, with various kernel versions.
Andreas.
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Andreas Schwab, SuSE Labs, [email protected] SuSE GmbH, Deutschherrnstr. 15-19, D-90429 Nürnberg Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different."
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Quoted 1 line · Peter Chubb
Peter> NTP on Linux 2.4.17/IA64 appears broken. ntpd never seems to Peter> be able to pull the PLL into sync, even after using ntpdate Peter> to set the clock to the correct server time.
Peter> What are other peoples' experiences with NTP on IA64?
I'm not aware of any problems with NTP keeping in sync with realtime. However, I do think the drift on the kernel's time-of-day (without NTP synchronization) may be bigger than it could be. This could be due to rounding errors, due to the CPU clock not being accurate enough, or something else entirely. Some time ago, I did look over the code and didn't find any obvious rounding errors, but that doesn't mean they don't exist. Actually, one experiment that might be worth doing is to set HZ to 100. This will make maintaining the time-of-day slightly easier and since it also happens to be the freq used by x86, makes it almost certain that there are no other subtle issues.
--david
I compared a HZ0 kernel with a HZ24 kernel on a BigSur ... it made no obvious difference, both kernels lost time at about 38.5 milliseconds/minute relative to a machine running NTP.
-Tony
-----Original Message-----
From: David Mosberger [mailto:[email protected]]
Sent: Friday, May 24, 2002 7:33 PM
To: Peter Chubb
Cc: [email protected]
Subject: Re: [Linux-ia64] NTP broken?
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On Wed, 22 May 2002 13:08:08 +1000, Peter Chubb
<[email protected]> said:
Peter> NTP on Linux 2.4.17/IA64 appears broken. ntpd never seems to Peter> be able to pull the PLL into sync, even after using ntpdate Peter> to set the clock to the correct server time.
Peter> What are other peoples' experiences with NTP on IA64?
I'm not aware of any problems with NTP keeping in sync with realtime. However, I do think the drift on the kernel's time-of-day (without NTP synchronization) may be bigger than it could be. This could be due to rounding errors, due to the CPU clock not being accurate enough, or something else entirely. Some time ago, I did look over the code and didn't find any obvious rounding errors, but that doesn't mean they don't exist. Actually, one experiment that might be worth doing is to set HZ to 100. This will make maintaining the time-of-day slightly easier and since it also happens to be the freq used by x86, makes it almost certain that there are no other subtle issues.
--david
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Quoted 1 line · Tony
Tony> I compared a HZ0 kernel with a HZ24 kernel on a BigSur Tony> ... it made no obvious difference, both kernels lost time at Tony> about 38.5 milliseconds/minute relative to a machine running Tony> NTP.
Hmmh, interesting data. So the rate is 633ppm. Does anyone know what the crystals on the BigSurs are rated at?
--david
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"David" = David Mosberger <[email protected]> writes:
On Wed, 22 May 2002 13:08:08 +1000, Peter Chubb <[email protected]> said:
Peter> NTP on Linux 2.4.17/IA64 appears broken. ntpd never seems to Peter> be able to pull the PLL into sync, even after using ntpdate to Peter> set the clock to the correct server time.
Peter> What are other peoples' experiences with NTP on IA64?
David> I'm not aware of any problems with NTP keeping in sync with David> realtime.
OK, I now have two i2000s both running the same kernel, both configured identically. On one of them, NTP pulls into sync within a few minutes. The other just drifts further and further away.
One interesting `feature' is that on the one that keeps running away, the CPU clock is detected as 718.793988 MHz not the supposedly correct 733MHz. The boot message says:
CPU 0: base freq0.684MHz, ITC ratio/2, ITC freqq8.764MHz
My suspicion is that this is incorrect on this machine, and it is *really* at 733MHz --- which would explain the lack of sync (NTP just can't slow the clock down enough) and the runaway time (733/718 is around 1.02; which corresponds to a second a minute)
The BIOS reports 733MHz, though.
Peter C
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"Peter" = Peter Chubb <[email protected]> writes:
"David" = David Mosberger <[email protected]> writes:
On Wed, 22 May 2002 13:08:08 +1000, Peter Chubb <[email protected]> said:
Peter> One interesting `feature' is that on the one that keeps running Peter> away, the CPU clock is detected as 718.793988 MHz not the Peter> supposedly correct 733MHz.
Guess what. After the reboot that I did to find out what the BIOS said, the kernel now reports the correct cpu clock frequency, and NTP works.
Peter C
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Quoted 1 line · Peter Chubb
Peter> Guess what. After the reboot that I did to find out what the Peter> BIOS said, the kernel now reports the correct cpu clock Peter> frequency, and NTP works.
Are you running the latest firmware? The clockfrequency is indeed _measured_ by the firmware and there used to be occasional but large errors in that measurement. I thought newer firmware doesn't have this problem any longer. So, if you're not running the latest version yet, it might be worth to update the firmware.
--david
David, FYI, I asked our hardware designers about current oscillator accuracy and was a bit suprised to learn that one pays a premium price today to get 300ppm. 600ppm can happen
in lower cost units.
FYI, Rich
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Quoted 2 lines · Tony
Tony> I compared a HZ0 kernel with a HZ24 kernel on a BigSur Tony> ... it made no obvious difference, both kernels lost time at Tony> about 38.5 milliseconds/minute relative to a machine running Tony> NTP.
Hmmh, interesting data. So the rate is 633ppm. Does anyone know what the crystals on the BigSurs are rated at?
--david_______________________________________________
Linux-IA64 mailing list
[email protected]
http://lists.linuxia64.org/lists/listinfo/linux-ia64
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Quoted 1 line · Rich Altmaier
Rich> David, FYI, I asked our hardware designers about current Rich> oscillator accuracy and was a bit suprised to learn that one Rich> pays a premium price today to get 300ppm. 600ppm can happen Rich> in lower cost units.
Thanks for sharing that. I just tried the obvious google search for "crystal ppm" and most of the hits where for crystals on the order of 30-50ppm, with the occasional 100ppm. Precision crystals seem to be rated at <1ppm. So, 600ppm seems a bit on the high side, but I guess it's not totally unreasonable either. I guess NTP is our friend... ;-)
--david