[Aptitude-devel] Strange issue with aptitude causing 100% cpu usage on Sid amd64 DomU

[Jö Fahlke]

Am Wed,  4. Jul 2012, 00:47:06 +0200 schrieb Axel Beckert:
> since about a day or such my Sid DomU (Xen virtual machine) gets
> extremely sluggish as soon as I start "aptitude -u". It even throws
> kernel messages like this several times during the (very slow) package
> update:
> 
> Message from syslogd at kiva6 at Jul  4 00:02:00 ...
>  kernel:[7736331.176014] BUG: soft lockup - CPU#0 stuck for 23s! [ksoftirqd/0:3]
> 
> aptitude (0.6.8) consumes 100% cpu according to htop and so do other
> processes (irssi, screen, htop itself, ksoftirqd/0 and a few more),
> load goes up to 4 to 7 and everything is very laggy. But as soon as
> suspend aptitude with Ctrl-Z or stop it with Ctrl-C, everything is
> fine again immediately.

Maybe this is due to the recent leap second problem[1].  Try setting the date
("date -s now") or rebooting.

[1] http://serverfault.com/questions/403732/anyone-else-experiencing-high-rates-of-linux-server-crashes-during-a-leap-second

Summary as far as I understand the problem: Leap second code in the kernel was
buggy in such a way that two kernel clocks will go out-of-sync by one second
when a leap second occurs.  If any program sets a timer for unter one second,
the timer will immediately fire.  Since timers may fire early for various
reasons, many programs will check for this and restart the timer, resulting in
a busy wait.  Setting the time with "date -s" brings the in-kernel clocks back
into sync.

Bye,
Jö.

-- 
Jorrit (Jö) Fahlke, Interdisciplinary Center for Scientific Computing,
Heidelberg University, Im Neuenheimer Feld 368, D-69120 Heidelberg
Tel: +49 6221 54 8890 Fax: +49 6221 54 8884

This is the first age that's paid much attention to the future, which
is a little ironic since we may not have one.
-- Arthur C Clarke
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