Re: kern/56322: Excessive clock drift

[Frank Kardel <kardel%kardel.name@localhost>]

The following reply was made to PR kern/56322; it has been noted by GNATS.

From: Frank Kardel <kardel%kardel.name@localhost>
To: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/56322: Excessive clock drift
Date: Thu, 22 Jul 2021 07:47:33 +0200

 Can you post
 
 sysctl kern.timecounter
 ?
 
 I assume the with the
 
 ERROR: 2607 cycle TSC drift observed
 
 TSC was not picked as timecounter on your system.
 
 Can you try
 
 sysctl -w kern.timecounter.hardware=i8254
 
 and see whether that improves the situation.
 
 I agree that ntpd is unlikely to curb that large drift.
 
 ntpd will on correct a drift up to 43 seconds per day (500ppm).
 
 Frank
 
 On 07/22/21 02:15, dholland%NetBSD.org@localhost wrote:
 >> Number:         56322
 >> Category:       kern
 >> Synopsis:       Excessive clock drift
 >> Confidential:   no
 >> Severity:       serious
 >> Priority:       medium
 >> Responsible:    kern-bug-people
 >> State:          open
 >> Class:          sw-bug
 >> Submitter-Id:   net
 >> Arrival-Date:   Thu Jul 22 00:15:00 +0000 2021
 >> Originator:     David A. Holland
 >> Release:        NetBSD 9.99.85 (20210623)
 >> Organization:
 >> Environment:
 > System: NetBSD valkyrie 9.99.85 NetBSD 9.99.85 (VALKYRIE) #7: Wed Jun 23 18:32:25 EDT 2021  dholland@valkyrie:/usr/src/sys/arch/amd64/compile/VALKYRIE amd64
 > Architecture: x86_64
 > Machine: amd64
 >> Description:
 > Four days ago (and a couple hours) I noticed the clock was badly
 > behind, and synced it with ntpdate.
 >
 > It is now on the order of 1:30 (that's one and a half minutes) behind,
 > by comparison to another machine that runs ntpd. This machine does
 > not, for no particular reason.
 >
 > This is a regression - prior to updating to 9.99.85 the clock lagged
 > but nowhere near so much.
 >
 > This is the relevant material I see in dmesg, which isn't much use.
 >
 > [     1.000000] timecounter: Timecounters tick every 10.000 msec
 > [     1.000000] timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
 > [     1.000003] timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
 > [     1.051023] timecounter: Timecounter "TSC" frequency 3517182870 Hz quality 3000
 >
 > Before this update I used to get messages of the form
 >     autoconfiguration error: ERROR: 2607 cycle TSC drift observed
 >
 > These have gone away, but I suspect the underlying problem is that the
 > TSC is bad and this is no longer being detected.
 >
 > Machine is a 6-way AMD Family 15h.
 >
 > I don't want to be fixing the time regularly because I'm sure it will
 > regularly remind me of PR 56097. I could turn on ntpd, but that's at
 > best a bandaid, and with this much drift it might just lose sync
 > anyway.
 >
 >> How-To-Repeat:
 >> Fix: