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Re: [Xen-devel] [PATCH RFC v1 4/4] libxc for rt scheduler

On gio, 2014-07-17 at 18:16 -0400, Meng Xu wrote:
> Hi Ian and George,
> George Dunlap <George.Dunlap@xxxxxxxxxxxxx>ä2014å7æ17æææååéï
>         On Thu, Jul 17, 2014 at 4:29 PM, Ian Campbell
>         <Ian.Campbell@xxxxxxxxxx> wrote:
>         > On Fri, 2014-07-11 at 16:49 +0200, Dario Faggioli wrote:
>         >
>         >> So, the bouncing logic seems fine. Looking at what other
>         schedulers do,
>         >> there should be no particular need for bouncing anything.
>         >
>         > Seems like there is some confusing precedent around the use
>         of sysctl vs
>         > domctl for sched parameters here.
>         >
>         > Most schedulers use domctl but arinc uses sysctl.
>         They're controlling different things.
>         domctl is controlling parameters related to *a particular
>         domain* (for
>         instance, weight or cap); sysctl is relating to setting
>         parameters
>         *for the scheduler as a whole* (for example, timeslice).
> Do we have to use inline parameters in domctl?  
I think you should use inline parameters as much as possible. Of course,
if you need to transfer the parameters for N vcpus (of the same domain)
all at once, you can use an array (i.e., an handle, of course), but only
for those parameters.

So, if you, for instance, you can have something like this:

    integer: num_vcpus
    array[]: { time_t: budget, time_t: period }

This, in case you want to batch the transfer of all the parameters for
all the vcpus in one hcall. BTW, I'm not sure you need num_vcpu to be
there, it depends if you have it available already from other hcall
performed before, etc.

For an hypercall that only retrieve the parameters for _one_ _vcpu_, it
should be something like this:

    time_t budget
    time_t period

(forgive the meta-language)

You don't have to implement the second hypercall if you think we don't
need it for now, it was just an example.

> Right now, we used the domctl to set/get the parameters of each vcpu
> of a domain. So from what the functionality does, it should be in
> domctl.  If we don't have to use inline parameters, I would prefer to
> use domctl. :-)
You shall use domctl! :-)


<<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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