[Xen-devel] wget and Zope crashes on post-2.0.6 -testing

[Osma Suominen <osma.suominen@xxxxxxxxxxxx>]

Hello,

I reported about time-related problems some days ago, with no replies:
http://thread.gmane.org/gmane.comp.emulators.xen.devel/10628

I have problems with e.g. wget and Zope crashing on domU on a recent 
-testing build. This is on a Debian Sarge system, with kernel 2.6.11.11 
and a Xen -testing snapshot from two days ago (2005-05-31). The problems 
are not as easy to trigger as with earlier versions (e.g. the 2.0.5 demo 
CD), but they do happen.
The symptom is that during heavy load, wget crashes with the message 
"acalc_rate: Assertion `msecs >= 0' failed", which probably means that 
time has stepped backwards (looking at earlier xen-devel posts).
Also, Zope frequently dies with different time-related error messages. 
Here's the end of a typical traceback:
  File "/usr/lib/zope2.7/lib/python/DateTime/DateTime.py", line 694, in 
_parse_args
    lt = safelocaltime(t)
  File "/usr/lib/zope2.7/lib/python/DateTime/DateTime.py", line 437, in 
safelocaltime
    raise TimeError, 'The time %f is beyond the range ' \
TimeError: The time nan is beyond the range of this Python implementation.

It is fairly easy to crash Zope this way by using a tool such as apache's 
benchmarking utility ab/ab2 or wget to pound on it. It usually takes a few 
minutes on an otherwise unloaded machine to bring down Zope. Note that 
Zope runs just fine on a similar native Linux system, and after running 
production Zope systems for more than a year, I have never seen the kind 
of errors Zope on Xen brings up.
To cause the wget error (which I think is a symptom of a very similar 
problem), it is easiest to run SETI@Home which will put enough load on the 
system. It might take a few attempts but I can always crash wget this way 
when SETI is running.
It is my impression that these problems occur during bursts of high timer 
interrupt activity, but I haven't made detailed studies.
Is there anything I can do to help sort out this? For example, would it be 
a good idea to test unstable to see if it exhibits this behavior? Any help 
is appreciated, and since I soon need to run a production Zope system on 
several Xen hosts, I would like to find a solution to the frequent 
crashes.
-Osma

--
*** Osma Suominen / MB Concert Ky *** osma.suominen@xxxxxxxxxxxx ***

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