Re: [Xen-devel] Time went backwards

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 10 Mar 2006, at 17:14, Keir Fraser wrote:

> > I am very frequently seeing these Time went backwards messages
> > on my test systems.  Running a 2 VCPU guest on a single CPU
> > computer seems to be effective at triggering this ;)
> That's interesting, particularly if you can trigger on a single 
> physical CPU. In that case cpu_delta should definitely *never* be 
> negative. Maybe the steal_time logic, which does mess with per-cpu 
> processed_system_time, is not quite right? :-)
To that end, it would be interesting to see if after the first do-while 
loop in timer_interrupt(), you can end up with sched_time > 
(processed_system_time + delta).
If so, we could end up running per-cpu processed_system_time ahead of 
current system time and so get -ve delta the *next* time we run 
timer_interrupt().
 -- Keir


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