[Xen-bugs] [Bug 1098] [version 3.1.0_15042-51] clocksource/0: Time went backwards

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1098





------- Comment #4 from ian.marlier@xxxxxxxxxxxxxxxxxxx  2007-10-31 13:52 
-------
> This is my guess.
> 
> You should test with vcpu pin. It would also solve this problem.
> If my guess is correct, You shoud fix xen_clocksource_read() increment
> monotonically.
> currently vcpu migration causes time went backwards.
> 

I tested the system, following this advice, and there was no change in
behavior.

I pinned the CPU's this way:
offxen2:~ # xm vcpu-list
Name                              ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0                           0     0     0   -b-    1146.3 0
Domain-0                           0     1     1   r--      93.8 1
Domain-0                           0     2     2   -b-     234.5 2
Domain-0                           0     3     3   -b-    1022.0 3
SUDCX                              2     0     0   -b-      26.8 0
SUDCX                              2     1     1   -b-      27.3 1
SUDCX                              2     2     2   -b-      21.3 2
SUDCX                              2     3     3   -b-      15.9 3
alpharobot                         1     0     0   -b-      58.3 0
alpharobot                         1     1     1   -b-      55.2 1
mx1                                3     0     2   -b-      10.9 2
mx1                                3     1     3   -b-       7.5 3

And left the clocksource set to "xen" -- I rebooted the machine so it was in a
fully default state.
offxen2:~ # cat
/sys/devices/system/clocksource/clocksource0/current_clocksource 
xen 

The VMs started up without trouble.

As soon as I began burn-in testing in one of the domains, occasional messages
started appearing in the logs about time going backward.

>From the time that I got the burn-in tests going on all four of the domains,
the messages were appearing 100 or more times per minute.  After approximately
9 minutes of burnin testing in all four domains, the machine became
unresponsive at the console and to network, and had to be hard reset.

So, it appears that vcpu-pin does not have any effect on this issue.


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