The day that time stood still

No, it’s not about that episode of “Supercar” from 1962. It’s about why running stock Xen-enabled Ubuntu 2.6.22 x86_64 kernel is generally a Bad Idea™:

So, you log into your dom0 on your regular Ubuntu compute cluster just to find out that all your users’ passwords have expired and the kernel is greeting you with messages from the distant future (Mon Apr 29 03:21:20 EET 2301 in that particular case):

[214464.660028] clocksource/1: Time went backwards: delta=–9223012651229942015 shadow=214463864019492 offset=796007077
[214469.660023] printk: 9970 messages suppressed.
[214469.660030] clocksource/4: Time went backwards: delta=–9223012646229940943 shadow=214468860019731 offset=800008116
[214474.660035] printk: 10051 messages suppressed.
...

Then you find out that most processes are using NaN percents of CPU, while others are using only 9999%:

../images/76.thumbnail.png

The day that time stood still

Not to mention the negative uptime…

Way to panic? Already reaching for the power switch? Trying to reboot? But all you have to do is to first:

echo "jiffies" > /sys/devices/system/clocksource/clocksource0/current_clocksource

and then think of either recompiling a better Xen-enabled kernel or (like me) switching to an alternative virtualisation solution.

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