Re: PV guest timings

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

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On mer, 2013-11-27 at 02:36 +0000, Simon Martin wrote:

> >  
> > Is there any chance that you can share/show it? At least the
> > relevant 
> > chunks... 
> No problems, I can share the complete code it you want, there is
> nothing proprietary in there yet. What's the best way to do it? Put it
> on github? Send a tarball?
>
Well, I think a repo somewhere would be preferrable over a tarball,
espacially if you have it in a (although private) repo already, so that
we gt to see the history, the commit changelogs, etc.

Also, if you go for github, or whatever similar service, people would be
able to both checkout your code, or browse it on-line, depending on what
they like most.

If you don't, I still personally prefer repositories, but, really,
whatever you're more comfortable with would do.

> > Some questions: 
> >  - "looking at the statistics", what statistics? How do you collect 
> >    them? 
> At every cycle I compare the current time with the expected time and
> calculate latency (time from when I expect the event to when it
> actually happens) and period.
>  
Sure, that part I got. I was more asking how you get these numbers out,
i.e., you print them online, store somewhere and print later/on request,
etc. (I guess I could have specified this more clearly, sorry about
that :-) )

> >  - you say you get latencies in some range and periods in some
> > other 
> >    range. It may be my fault, but I'm not sure I understand what
> > you 
> >    mean with these two terms in this context, could you clarify? 
> >   
> Latency = difference between expected time and actual time of the
> event.
>  
> Period = time between two consecutive events. 
>
Ok, I think I see now. Just to confirm that I do, this means that the
values/ranges you get by measuring both are related, i.e., not
completely independent, right? Again, I'm not saying it's not useful to
have both, just trying to double check I understood what you're doing.

> > I'm not sure if fits your exact needs, and you probably know it
> > already, 
> > but, just in case, have you looked at xentrace and xenalyze? There's
> > a 
> > blog post that could be a nice introduction to them: 
> > http://blog.xen.org/index.php/2012/09/27/tracing-with-xentrace-and-xenalyze/ 
> >  
> I hadn't read that. I'll look at it tomorrow (it's almost midnight
> here).
>  
Ask again if you need anything.

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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