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Re: [Xen-devel] Time went backwards

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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