Re: [Xen-users] clocksource/0: Time went backwards

[Bart Verwilst <lists@xxxxxxxxxxx>]

In the meantime i switched back to the normal clocksource.

But i just might have found the something interesting..
This morning, i wanted to check my mails ( which run in a domU ). I noticed i 
couldn't get to it, "Unable to connect", as usual.. But i had cacti open, which 
could read snmp from the server just fine.
I logged in through SSH, and noticed that the date was set to "Fri Dec 22 
22:49:54 CET 2226", and not going forward anymore. The clock had stopped.

In the meantime, /var/log/messages was spewing messages like this:

[134918.952935] clocksource/0: Time went backwards: delta=-6917269600674797899 
shadow=134918109266738 offset=843667158
[134923.954592] printk: 1157408 messages suppressed.
[134923.954606] clocksource/0: Time went backwards: delta=-6917269595673126078 
shadow=134923109294656 offset=845310074
[134928.952308] printk: 1154382 messages suppressed.
[134928.952323] clocksource/0: Time went backwards: delta=-6917269590675409336 
shadow=134928109321066 offset=842999953

I decided to change something to see if it works, so i did:
cat /sys/devices/system/clocksource/clocksource0/current_clocksource, which 
showed "xen" as usual.
I then did
echo "jiffies" > 
/sys/devices/system/clocksource/clocksource0/current_clocksource, which 
instantly made my clock run again, and stalled programs revived. I saw my 
webmail ( which was still hanging all the time ) spring to life, along with my 
previously entered reboot command..

Does this narrow down the search to the solution?

Kind regards,

Bart


----- Original Message -----
From: "Bart Verwilst" <lists@xxxxxxxxxxx>
To: "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxx>
Cc: Xen-users@xxxxxxxxxxxxxxxxxxx
Sent: Thursday, October 11, 2007 3:55:28 PM (GMT+0100) Europe/Berlin
Subject: Re: [Xen-users] clocksource/0: Time went backwards

Another thing i just tried is this:

# cat /sys/devices/system/clocksource/clocksource0/current_clocksource
xen 
# cat /sys/devices/system/clocksource/clocksource0/available_clocksource 
xen jiffies 
# echo jiffies > 
/sys/devices/system/clocksource/clocksource0/current_clocksource

In dmesg:

[57990.836097] Time: jiffies clocksource has been installed.

Do you think this might work? Will it break something else? Is this a good idea?

Thanks!

Bart Verwilst

----- Original Message -----
From: "Samuel Thibault" <samuel.thibault@xxxxxxxxxxxx>
To: "Bart Verwilst" <lists@xxxxxxxxxxx>
Cc: Xen-users@xxxxxxxxxxxxxxxxxxx
Sent: Thursday, October 11, 2007 3:19:37 PM (GMT+0100) Europe/Berlin
Subject: Re: [Xen-users] clocksource/0: Time went backwards

Bart Verwilst, le Thu 11 Oct 2007 15:12:19 +0200, a Ãcrit :
> Oh.. i was hoping for some simple sysctl tweak or easy patch :)
> Bummer :(

Oh, actually, the problem you're getting might be related to CPU
frequency changes, try to disable that as well.

Samuel


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