Re: PV guest timings

[Dario Faggioli <dario.faggioli@citrix.com>]

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On mer, 2013-11-27 at 02:32 +0000, Simon Martin wrote:
>  
> > On mar, 2013-11-26 at 15:38 +0000, Simon Martin wrote: 
> >  
> >  
> > >  As an additional comment. I decided to filter out the samples
> > > with 
> > >  negative latency. This seems to happen 100 times a second, i.e.
> > > the 10 
> > >  ms Hypervisor timer event. 
> > >  
> > Again, what's "negative latency" ? 
>
> Latency is the time between the deadline and the handler being called.
>
Ok, that's a reasonable definition of latency. However, if you don't
mind another question, 'deadline' here is basically the deadline of the
periodic instance x-1, and you expect a timer firing at that time in
order to activate instance x? Or is that a proper deadline (and the
above is just called period) and you want to have some handler running
when it's missed?

>  Negative latency means the handler was called before the next
> deadline.
>  
Oh, wow... I see. So you're saying that you have timers firing early
than their expiry time? Is that expected? Why is that happening? :-O

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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