Re: xen 4.5.0 rtds scheduler perform poorly with 2vms

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

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On Sun, 2015-11-29 at 11:44 -0500, Meng Xu wrote:
> 2015-11-29 11:27 GMT-05:00 Dario Faggioli <dario.faggioli@citrix.com>
> :
> > 
> > Mmmm... As I said many times, I don't remember much of all those RT
> > schedulability formulas, but, is really that simple?
> 
> Ah, let me clarify...
> It is not that simple. ;-) I just simplify it, hoping it can simplify
> the problem and highlight the possible reason.
> 
Ok, glad to know I haven't completely lost my mind, or anything like
that! :-)

> > I mean, if the in-
> > guest scheduling algorithm is global (e.g., global-EDF), the task
> > could
> > migrate, couldn't it?
> 
> Yes. If these partial VCPUs happen to be scheduled "sequentially",
> the
> OS inside VM can migrate the task and make the task keep running. But
> that is not the worst-case for the OS.
> 
Right, I see it now, and (FWIW) I absolutely agree with the worst-case
analysis you provided (thanks). I did not get the fact that you were
talking about the worst-case, sorry for the noise. :-D

> The detailed illustration of the worst case scenario is at Arvind's
> paper: http://link.springer.com/article/10.1007%2Fs11241-009-9073-x
> My latest journal paper
> (http://link.springer.com/article/10.1007%2Fs11241-015-9223-2)
> tighten
> the resource supply bound function of the MPR model. I believe the
> equations are too boring to most of people in the mailing list.
> 
> So let's avoid the complex equations here. ;-)
> 
Thanks for this too! :-)

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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