Home » Mailing list archives » linux-kernel » 2007 » September » 3

System clock frequency offset changes drastically across reboots

!MAILaRCHIVE_VOTE_RePLACE
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
[view in full thread]
From: John Sigler <linux.kernel@...>
To: <linux-kernel@...>, linux-rt-users <linux-rt-users@...>
Cc: <johnstul@...>, <tglx@...>
Subject: System clock frequency offset changes drastically across reboots
Date: Monday, September 3, 2007 - 6:21 am

[ Re-sending... Please feel free to comment, even if you don't have
"The Solution". I'd just like to get some feedback. ]

Hello everyone,

I'm using 2.6.20.7-rt8 on a P3.

I've noticed that the frequency offset of my system clock (computed
either by ntpd, or by hand) changes drastically across reboots.

By drastically, I mean +/- 60 ppm every time I reboot.

Apparently this is caused by some imprecision in the frequency
estimation done in calculate_cpu_khz() (arch/i386/kernel/tsc.c)

My brutally crude work-around was to skip the computation altogether and
hard-code the "correct" value for cpu_khz.

http://linux.kernel.free.fr/cpu_khz.adlink

Has this issue been investigated more thoroughly by other users?

Regards.

-
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
Messages in current thread:
System clock frequency offset changes drastically across reb..., John Sigler, (Mon Sep 3, 6:21 am)