Re: [Xen-devel] Time went backwards

[Rik van Riel <riel@xxxxxxxxxx>]

On Fri, 10 Mar 2006, Keir Fraser wrote:
> On 10 Mar 2006, at 17:00, Rik van Riel 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? :-)

My current suspicion is that the per-cpu processed_system_time
gets incremented twice during one timer irq handling, and then
we notice it was incremented too far during the _next_ timer
interrupt.

> When did you start seeing the messages?

They became frequent after the new steal time code went in.

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