Re: [PATCH v1 1/4] xen: add real time scheduler rt

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

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On mer, 2014-09-03 at 10:24 -0400, Meng Xu wrote:

> 2014-09-03 10:08 GMT-04:00 George Dunlap
> <George.Dunlap@eu.citrix.com>:

>         Under what circumstances would anyone want a period of an
>         hour?
>         ​ ​
>         At
>         this point we're talking about a vcpu being allowed to run
>         continuously without pre-emption for half an hour, and then
>         not
>         *allowed* to run at all for another half hour.  That just
>         seems really
>         ridiculous.
> 
> 
> ​Honestly speaking, I don't think setting period and budget to hours
> is a good idea
> ​ either. ​
>  
Indeed, it makes no sense to me too.

> How about this:
> I change the type to uint32 bit and use 2^32us ~= 1.19h as the upper
> bound of period and budget. 
>
Fine for me.

> ​I document the range of period and budget on the website and also let
> users know how to scale down the parameters of vcpus in case they have
> a very large period and budget.
> 
I guess something like that won't harm on any website (BTW, are you
talking about RT-Xen website? Xen Wiki? Both? :-D). In the code, I won't
"waste" to much line of comments on this. I don't see any special need
for explaining the scaling down either, it's pretty straightforward once
you have even a very light knowledge of what the scheduling algorithm
does (like the bare minimum you need for being able to use it!).

Just make sure that you specify, especially in public headers of all the
various components (so Xen, libxc and libxl) what the time unit is, that
is _the_ important piece of information one needs to use the scheduler
properly.

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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